Publications by authors named "Ian Baker"

49 Publications

Understanding water and energy fluxes in the Amazonia: Lessons from an observation-model intercomparison.

Glob Chang Biol 2021 Feb 10. Epub 2021 Feb 10.

Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ, USA.

Tropical forests are an important part of global water and energy cycles, but the mechanisms that drive seasonality of their land-atmosphere exchanges have proven challenging to capture in models. Here, we (1) report the seasonality of fluxes of latent heat (LE), sensible heat (H), and outgoing short and longwave radiation at four diverse tropical forest sites across Amazonia -- along the equator from the Caxiuanã and Tapajós National Forests in the eastern Amazon to a forest near Manaus, and from the equatorial zone to the southern forest in Reserva Jaru; (2) investigate how vegetation and climate influence these fluxes; and (3) evaluate land surface model (LSM) performance by comparing simulations to observations. We found that previously identified failure of models to capture observed dry-season increases in evapotranspiration was associated with model over-estimations of (1) magnitude and seasonality of Bowen ratios (relative to aseasonal observations in which sensible was only 20-30% of the latent heat flux) indicating model exaggerated water limitation, (2) canopy emissivity and reflectance (albedo was only 10 to 15% of incoming solar radiation, compared to 0.15-0.22% simulated), and (3) vegetation temperatures (due to underestimation of dry-season evapotranspiration and associated cooling). These partially compensating model-observation discrepancies (e.g. higher temperatures expected from excess Bowen ratios were partially ameliorated by brighter leaves and more interception/evaporation) significantly biased seasonal model estimates of net radiation (Rn), the key driver of water and energy fluxes (LE ~ 0.6Rn and H ~ 0.15Rn). Though these biases varied among sites and models. A better representation of energy-related parameters associated with dynamic phenology (e.g. leaf optical properties, canopy interception, and skin temperature) could improve simulations and benchmarking of current vegetation-atmosphere exchange and reduce uncertainty of regional and global biogeochemical models.
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http://dx.doi.org/10.1111/gcb.15555DOI Listing
February 2021

Young-onset frontotemporal dementia with FUS pathology.

Pract Neurol 2020 Dec 11. Epub 2020 Dec 11.

Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, Oxfordshire, UK.

Frontotemporal dementia (FTD) is an uncommon cause of behavioural change in adults under the age of 50. A 44-year-old man presented with progressive neuropsychiatric disturbance characterised by social withdrawal, apathy, loss of empathy, motor stereotypies and hyperorality. Cognitive testing identified severe impairment, including executive dysfunction. MR scan of the brain showed bilateral symmetrical frontal atrophy. There was no relevant family history, and targeted genetic testing for FTD-associated variants in , and genes proved negative. He became more withdrawn with disinhibited behaviour; his condition progressively worsened and he died 6 years later. The pathological diagnosis was frontotemporal lobar degeneration with fused-in-sarcoma (FUS) pathology, a rare sporadic cause of FTD, accounting for only 5%-10% of cases, its characteristic features including very young onset, motor stereotypies and hyperorality.
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http://dx.doi.org/10.1136/practneurol-2020-002730DOI Listing
December 2020

Spring enhancement and summer reduction in carbon uptake during the 2018 drought in northwestern Europe.

Philos Trans R Soc Lond B Biol Sci 2020 10 7;375(1810):20190509. Epub 2020 Sep 7.

Meteorology and Air Quality, Wageningen University and Research, Wageningen, The Netherlands.

We analysed gross primary productivity (GPP), total ecosystem respiration (TER) and the resulting net ecosystem exchange (NEE) of carbon dioxide (CO) by the terrestrial biosphere during the summer of 2018 through observed changes across the Integrated Carbon Observation System (ICOS) network, through biosphere and inverse modelling, and through remote sensing. Highly correlated yet independently-derived reductions in productivity from sun-induced fluorescence, vegetative near-infrared reflectance, and GPP simulated by the Simple Biosphere model version 4 (SiB4) suggest a 130-340 TgC GPP reduction in July-August-September (JAS) of 2018. This occurs over an area of 1.6 × 10 km with anomalously low precipitation in northwestern and central Europe. In this drought-affected area, reduced GPP, TER, NEE and soil moisture at ICOS ecosystem sites are reproduced satisfactorily by the SiB4 model. We found that, in contrast to the preceding 5 years, low soil moisture is the main stress factor across the affected area. SiB4's NEE reduction by 57 TgC for JAS coincides with anomalously high atmospheric CO observations in 2018, and this is closely matched by the NEE anomaly derived by CarbonTracker Europe (52 to 83 TgC). Increased NEE during the spring (May-June) of 2018 (SiB4 -52 TgC; CTE -46 to -55 TgC) largely offset this loss, as ecosystems took advantage of favourable growth conditions. This article is part of the theme issue 'Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale'.
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http://dx.doi.org/10.1098/rstb.2019.0509DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7485100PMC
October 2020

Identification of a calcium phosphoserine coordination network in an adhesive organo-apatitic bone cement system.

Acta Biomater 2020 03 13;105:280-289. Epub 2020 Jan 13.

Thayer School of Engineering, Dartmouth College, Hanover, NH, United States.

Calcium phosphate-based bone cements have been widely adopted in both orthopedic and dental applications. Phosphoserine (pSer), which has a natural role in biomineralization, has been identified to possess the functionality to react with calcium phosphate phases, such as tetracalcium phosphate (TTCP) and α-tricalcium phosphate (α-TCP), and form a uniquely adhesive cement. This study investigated the chemical composition and phase evolution of a heterogeneous calcium phosphate (56% TTCP and 15% α-TCP) and pSer cement system with respect to pH. The coordination network of calcium phosphoserine monohydrate was discovered as the predominant crystalline phase of this adhesive apatitic cement system. Furthermore, it was determined that pH has a significant effect on the reaction kinetics of the system, whereby a lower pH tends to accelerate the reaction rate and favor products with lower Ca/P ratios. These findings provide a better understanding of the reaction and products of this adhesive organo-ceramic cement, which can be compositionally tuned for broad applications in the orthopedic and dental spaces. STATEMENT OF SIGNIFICANCE: The application of self-setting calcium phosphate cements (CPCs) in hard tissue regeneration has been a topic of significant research since their introduction to the field 30 years ago. Traditional CPCs, however, are limited by their suboptimal mechanical properties due to their solely inorganic composition. Recently, it was discovered that monomeric phosphoserine (pSer) is capable of serving as a setting reagent for a subset of CPC systems, resulting in an adhesive organo-ceramic composite. Despite its adhesive functionality and biomedical potential, its reaction chemistry and product composition were not well characterized. The present study identifies a calcium phosphoserine coordination network as the primary crystalline phase of this apatitic cement system and further characterizes compositional tunability of the products with respect to pH.
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http://dx.doi.org/10.1016/j.actbio.2020.01.007DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7134197PMC
March 2020

Surface-Atmosphere Coupling Scale, the Fate of Water, and Ecophysiological Function in a Brazilian Forest.

J Adv Model Earth Syst 2019 Aug 5;11(8):2523-2546. Epub 2019 Aug 5.

Atmospheric Science Department Colorado State University Fort Collins CO USA.

Tropical South America plays a central role in global climate. Bowen ratio teleconnects to circulation and precipitation processes far afield, and the global CO growth rate is strongly influenced by carbon cycle processes in South America. However, quantification of basin-wide seasonality of flux partitioning between latent and sensible heat, the response to anomalies around climatic norms, and understanding of the processes and mechanisms that control the carbon cycle remains elusive. Here, we investigate simulated surface-atmosphere interaction at a single site in Brazil, using models with different representations of precipitation and cloud processes, as well as differences in scale of coupling between the surface and atmosphere. We find that the model with parameterized clouds/precipitation has a tendency toward unrealistic perpetual light precipitation, while models with explicit treatment of clouds produce more intense and less frequent rain. Models that couple the surface to the atmosphere on the scale of kilometers, as opposed to tens or hundreds of kilometers, produce even more realistic distributions of rainfall. Rainfall intensity has direct consequences for the "fate of water," or the pathway that a hydrometeor follows once it interacts with the surface. We find that the model with explicit treatment of cloud processes, coupled to the surface at small scales, is the most realistic when compared to observations. These results have implications for simulations of global climate, as the use of models with explicit (as opposed to parameterized) cloud representations becomes more widespread.
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http://dx.doi.org/10.1029/2019MS001650DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6851591PMC
August 2019

Microstructural characterization of snow, firn and ice.

Authors:
Ian Baker

Philos Trans A Math Phys Eng Sci 2019 Jun;377(2146):20180162

Thayer School of Engineering, Dartmouth College , Hanover, NH 03755 , USA.

This paper provides an overview of techniques used to characterize the microstructure of snow, firn and ice. These range from traditional optical microscopy techniques such as examining thin sections between crossed polarizers to various electron-optical and X-ray techniques. Techniques that could have an impact on microstructural characterization of snow, firn and ice in the future are briefly outlined. This article is part of the theme issue 'The physics and chemistry of ice: scaffolding across scales, from the viability of life to the formation of planets'.
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http://dx.doi.org/10.1098/rsta.2018.0162DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6501914PMC
June 2019

Exploring the relationship between gamma-band activity and maths anxiety.

Cogn Emot 2019 Mar 18:1-11. Epub 2019 Mar 18.

a Psychology Department , University of Derby , Derby , UK.

Previous research has outlined high anxiety in connection with gamma modulation, identifying that gamma-band activity (40-100 Hz) correlates with processing of threat perception, attention and anxiety. Maths anxiety research has also noted the involvement of these aspects, yet this has not been investigated from a neurophysiological standpoint. Electroencephalography (EEG) was used to research gamma-band activity in relation to maths anxiety over two studies. The first measured gamma differences during the processing of complex addition and multiplication stimuli. Results identified differences between high and low maths anxious individuals; significantly greater gamma power was observed in those with high maths anxiety than those with low maths anxiety. As a control condition was not used, the second study replicated the design, but also applied a non-numerical control condition amongst the other stimuli sets. This showed significantly greater gamma activity in high maths anxious individuals across numerical conditions, but not in the non-numerical condition. High maths anxious individuals likely show attentional bias and threat perception to numerical-based stimuli, as indexed by gamma power. This study provides the first evidence of greater gamma-band activity in high maths anxious individuals and serves as a foundation for the exploration of gamma activity in high maths anxious individuals.
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http://dx.doi.org/10.1080/02699931.2019.1590317DOI Listing
March 2019

Lateral parietal contributions to memory impairment in posterior cortical atrophy.

Neuroimage Clin 2018 5;20:252-259. Epub 2018 Jul 5.

Nuffield Department of Clinical Neurosciences, University of Oxford, John Radcliffe Hospital, Oxford, UK.

Objective: Posterior cortical atrophy (PCA) is a neurodegenerative syndrome characterised by progressive impairment in visuospatial and perceptual function. Recent findings show that memory functioning can also be compromised early in the course of disease. In this study, we investigated the neural basis of memory impairment in PCA, and hypothesised that correlations would be observed with parietal cortex rather than classic medial temporal memory structures.

Methods: Eighteen PCA patients, 15 typical Alzheimer's disease (tAD) patients and 21 healthy controls underwent memory testing with the Rey Auditory Verbal Learning Test (RAVLT) word list and MRI. Voxel-based morphometry (VBM) was used to identify regions in the parietal and medial temporal lobes that correlated with memory performance.

Results: Compared with controls, PCA patients were impaired at learning, immediate and delayed recall and recognition of the RAVLT. Learning rate and immediate recall was significantly better in PCA compared to tAD, whereas there was no difference in delayed recall. Recognition memory also was not statistically different between patient groups, but PCA patients made significantly more false positive errors than tAD patients. VBM analysis in the PCA patients revealed a significant correlation between total learning and grey matter density in the right supramarginal gyrus, right angular gyrus and left postcentral gyrus. The left post central gyrus also significantly correlated with immediate and delayed recall and with recognition memory. No correlations were detected in the medial temporal lobe.

Conclusions: The findings provide novel evidence that early verbal memory impairment is frequently observed in PCA, and is associated with damage to lateral parietal structures. The results have implications for the diagnosis and management of PCA.
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http://dx.doi.org/10.1016/j.nicl.2018.07.005DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6080578PMC
January 2019

Association between precuneus volume and autobiographical memory impairment in posterior cortical atrophy: Beyond the visual syndrome.

Neuroimage Clin 2018 10;18:822-834. Epub 2018 Mar 10.

Nuffield Department of Clinical Neurosciences, University of Oxford, John Radcliffe Hospital, Oxford, UK.

Posterior cortical atrophy is a neurodegenerative syndrome characterised by progressive disruption of visual and perceptual processing, associated with atrophy in the parieto-occipital cortex. Current diagnostic criteria describe relative sparing of episodic memory function, but recent findings suggest that anterograde memory is often impaired. Whether these deficits extend to remote memory has not been addressed. A large body of evidence suggests that the recollection of an autobiographical event from the remote past coincides with the successful retrieval of visual images. We hypothesised that the profound visual processing deficits in posterior cortical atrophy would result in impaired autobiographical memory retrieval. Fourteen posterior cortical atrophy patients, eighteen typical Alzheimer's disease patients and twenty-eight healthy controls completed the Autobiographical Interview. Autobiographical memory in posterior cortical atrophy was characterised by a striking loss of internal, episodic detail relative to controls and to same extent as typical Alzheimer's disease patients, in conjunction with an increase in external details tangential to the memory described. The memory narratives of posterior cortical atrophy patients showed a specific reduction in spatiotemporal and perceptual detail. Voxel-based morphometry analysis revealed atrophy of the parieto-occipital cortices in posterior cortical atrophy but relatively spared hippocampi bilaterally, compared with characteristic atrophy of the medial temporal lobes in typical Alzheimer's disease. Analysis of brain regions showing posterior cortical atrophy-specific atrophy revealed a correlation between perceptual details in autobiographical memory and grey matter density in the right precuneus. This study demonstrates remote memory impairment in posterior cortical atrophy despite relatively preserved medial temporal lobe structures. The results demonstrate, for the first time, profound autobiographical memory impairment in PCA and suggest that this is driven by the well-recognised deficits in higher-order visual processing. The findings are discussed in the context of posterior parietal contributions to imagery and memory, and the clinical implications of autobiographical memory impairment for diagnostic and management protocols in posterior cortical atrophy.
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http://dx.doi.org/10.1016/j.nicl.2018.03.008DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5988022PMC
January 2019

Single-crystal ice surfaces unveil connection between macroscopic and molecular structure.

Proc Natl Acad Sci U S A 2017 05 9;114(21):5349-5354. Epub 2017 May 9.

Department of Chemistry, Laboratory for Water and Surface Studies, Tufts University, Medford, MA 02155;

Physics and chemistry of ice surfaces are not only of fundamental interest but also have important impacts on biological and environmental processes. As ice surfaces-particularly the two prism faces-come under greater scrutiny, it is increasingly important to connect the macroscopic faces with the molecular-level structure. The microscopic structure of the ubiquitous ice crystal is well-known. It consists of stacked layers of chair-form hexagonal rings referred to as molecular hexagons. Crystallographic unit cells can be assembled into a regular right hexagonal prism. The bases are labeled crystallographic hexagons. The two hexagons are rotated 30° with respect to each other. The linkage between the familiar macroscopic shape of hexagonal snowflakes and either hexagon is not obvious per se. This report presents experimental data directly connecting the macroscopic shape of ice crystals and the microscopic hexagons. Large ice single crystals were used to fabricate samples with the basal, primary prism, or secondary prism faces exposed at the surface. In each case, the same sample was used to capture both a macroscopic etch pit image and an electron backscatter diffraction (EBSD) orientation density function (ODF) plot. Direct comparison of the etch pit image and the ODF plot compellingly connects the macroscopic etch pit hexagonal profile to the crystallographic hexagon. The most stable face at the ice-water interface is the smallest area face at the ice-vapor interface. A model based on the molecular structure of the prism faces accounts for this switch.
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http://dx.doi.org/10.1073/pnas.1703056114DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5448200PMC
May 2017

Symptoms of anxiety and depression are related to cardiovascular responses to active, but not passive, coping tasks.

Braz J Psychiatry 2017 Apr-Jun;39(2):110-117. Epub 2016 Nov 7.

Centre for Psychological Research, Faculty of Education, Health and Sciences, University of Derby, United Kingdom.

Objective:: Anxiety and depression have been linked to blunted blood pressure (BP) and heart rate (HR) reactions to mental stress tests; however, most studies have not included indices of underlying hemodynamics nor multiple stress tasks. This study sought to examine the relationships of anxiety and depression with hemodynamic responses to acute active and passive coping tasks.

Methods:: A total of 104 participants completed the Hospital Anxiety and Depression Scales and mental arithmetic, speech, and cold pressor tasks while BP, HR, total peripheral resistance, and cardiac output (CO) were assessed.

Results:: After adjustment for traditional risk factors and baseline cardiovascular activity, depression scores were negatively associated with systolic BP, HR, and CO responses to the mental arithmetic task, while anxiety scores were inversely related to the systolic BP response to mental arithmetic.

Conclusion:: High anxiety or depression scores appear to be associated with blunted cardiac reactions to mental arithmetic (an active coping task), but not to the cold pressor test or speech tasks. Future research should further examine potential mechanisms and longitudinal pathways relating depression and anxiety to cardiovascular reactivity.

Clinical Trial Registration Number:: TCTR20160208004.
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http://dx.doi.org/10.1590/1516-4446-2016-1935DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7111443PMC
September 2017

Magnetic Heating of Fe-Co Ferrites: Experiments and Modeling.

Nano Life 2016 Jun 22;6(2). Epub 2016 Jun 22.

Thayer School of Engineering, Dartmouth College Hanover, NH 03755, U.S.A.

Magnetic nanoparticle hyperthermia uses magnetically-induced heat to kill cancer cells. In an alternating magnetic field, the induced heat depends strongly on particles' absorption properties. In order to achieve and maintain therapeutic temperatures inside a tumor and to minimize damage to normal tissues due to induced eddy currents, there is a need to develop new magnetic nanoparticles with improved heating characteristics. This paper investigates the magnetic heating properties of composite iron-cobalt ferrite nanoparticles Co Fe FeO with 0≤≤1. These composite materials are synthesized using a precipitation method. First, the Fe-Co nanoparticle synthesis is described, then their structure, size, magnetic and heating properties are measured and analyzed. The resulting nanoparticles were treated at temperatures 100-600°C in order to study any structural transformations and changes of physical properties. Finally, an empirical model is used to calculate both the nanoparticles' coercivity and their specific absorption rates for different Co concentrations.
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http://dx.doi.org/10.1142/S1793984416500070DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4998181PMC
June 2016

Diagnosing young onset dementia can be challenging.

Practitioner 2016 May;260(1793):11-7, 2

Although the risk of developing dementia increases with age, onset can be as early as the third or fourth decade of life. Genetic influences play a more important role in younger than in older people with dementia, so young onset dementia may cluster in families. Diagnosing young onset dementia is challenging. The range of possible presenting features is broad, encompassing behavioural, cognitive, psychiatric and neurological domains, and symptoms are often subtle initially. Frequently the complaints are misattributed to stress or depression, and the patient is falsely reassured that they are too young to have dementia. The most common causes of young onset dementia are early onset forms of adult neurodegenerative conditions and alcohol. Vascular dementia is the second most common cause of young onset dementia after Alzheimer's disease. Conventional vascular risk factors may be absent and diagnosis relies on imaging evidence of cerebrovascular disease. Obtaining a detailed history remains the most important part of the workup and usually requires corroboration by a third party. Undertaking a basic neurological examination is also important. Those with suspected young onset dementia should be referred to a neurology-led cognitive disorders clinic where available as the differenti diagnosis is considerably broader tha in older adults and requires specialist investigation.
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May 2016

Utility of testing for apraxia and associated features in dementia.

J Neurol Neurosurg Psychiatry 2016 Nov 1;87(11):1158-1162. Epub 2016 Jun 1.

Nuffield Department of Clinical Neurosciences, University of Oxford, John Radcliffe Hospital, Oxford, UK.

Introduction: Existing literature suggests that the presence or absence of apraxia and associated parietal deficits may be clinically relevant in differential diagnosis of dementia syndromes.

Aim: This study investigated the profile of these features in Alzheimer's disease (AD) and frontotemporal dementia (FTD) spectrum disorders, at first presentation.

Methods: Retrospective case note analysis was undertaken in 111 patients who presented to the Oxford Cognitive Disorders Clinic, Oxford, UK, including 29 amnestic AD, 12 posterior cortical atrophy (PCA), 12 logopenic primary progressive aphasia (lvPPA), 20 behavioural variant FTD (bvFTD), 7 non-fluent variant PPA (nfvPPA), 6 semantic variant PPA (svPPA) and 25 patients with subjective cognitive impairment (SCI). The clinical features of interest were: limb apraxia, apraxia of speech (AOS), and left parietal symptoms of dyslexia, dysgraphia, and dyscalculia.

Results: The prevalence of limb apraxia was highest in PCA, amnestic AD, lvPPA and nfvPPA. AOS was only observed in nfvPPA. Associated parietal features were more prevalent in AD spectrum than FTD spectrum disorders. Group comparisons between key differential diagnostic challenges showed that lvPPA and nfvPPA could be significantly differentiated on the presence of left parietal features and AOS, and amnestic AD could be differentiated from bvFTD, svPPA and SCI by limb apraxia. Regression analysis showed that limb apraxia could successfully differentiate between AD and FTLD spectrum disorders with 83% accuracy.

Discussion: Disease-specific profiles of limb apraxia and associated deficits can be observed. FTD and AD spectrum disorders can be difficult to differentiate due to overlapping cognitive symptoms, and measures of apraxia, in particular, appear to be a promising discriminator.
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http://dx.doi.org/10.1136/jnnp-2015-312945DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5099316PMC
November 2016

Memory Impairment at Initial Clinical Presentation in Posterior Cortical Atrophy.

J Alzheimers Dis 2016 04;52(4):1245-50

Nuffield Department of Clinical Neurosciences, University of Oxford, John Radcliffe Hospital, Oxford, UK.

Posterior cortical atrophy (PCA) is characterized by core visuospatial and visuoperceptual deficits, and predominant atrophy in the parieto-occipital cortex. The most common underlying pathology is Alzheimer's disease (AD). Existing diagnostic criteria suggest that episodic memory is relatively preserved. The aim of this study was to examine memory performance at initial clinical presentation in PCA, compared to early-onset AD patients (EOAD). 15 PCA patients and 32 EOAD patients, and 34 healthy controls were entered into the study. Patients were tested on the Addenbrooke's Cognitive Examination (ACE-R), consisting of subscales in memory and visuospatial skills. PCA and EOAD patients were significantly impaired compared to controls on the ACE total score (p < 0.001), visuospatial skills (p < 0.001), and memory (p < 0.001). Consistent with the salient diagnostic deficits, PCA patients were significantly more impaired on visuospatial skills compared to EOAD patients (p < 0.001). However, there was no significant difference between patient groups in memory. Further analysis of learning, recall, and recognition components of the memory subscale showed that EOAD and PCA patients were significantly impaired compared to controls on all three components (p < 0.001), however, there was no significant difference between EOAD and PCA patients. The results of this study show that memory is impaired in the majority of PCA patients at clinical presentation. The findings suggest that memory impairment must be considered in assessment and management of PCA. Further study into memory in PCA is warranted, since the ACE-R is a brief screening tool and is likely to underestimate the presence of memory impairment.
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http://dx.doi.org/10.3233/JAD-160018DOI Listing
April 2016

Do Cardiovascular Responses to Active and Passive Coping Tasks predict Future Blood Pressure over a 10-Month Later?

Span J Psychol 2016 Mar 14;19:E10. Epub 2016 Mar 14.

University of Derby(UK).

The study examined whether cardiovascular responses to active or passive coping tasks and single or multiple tasks predicted changes in resting blood pressure (BP) over a ten-month period. Heart rate (HR), BP, cardiac output (CO), and total peripheral resistance (TPR) were measured at rest, and during mental stress tests (mental arithmetic, speech, and cold pressor tasks). A total of 104 eligible participants participated in the initial study, and 77 (74.04%) normotensive adult participants' resting BP were re-evaluated at ten-month follow-up. Regression analyses indicated that after adjustment for baseline BP, initial age, gender, body mass index, family history of cardiovascular disease, and current cigarette smoking, heighted systolic blood pressure (SBP) and HR responses to an active coping task (mental arithmetic) were associated with increased future SBP (ΔR2 = .060, ΔR2 = .045, respectively). Further, aggregated SBP responsivity (over the three tasks) to the predictor models resulted in significant, but smaller increases in ΔR2 accounting for .040 of the variance of follow-up SBP. These findings suggest that cardiovascular responses to active coping tasks predict future SBP. Further, compared with single tasks, the findings revealed that SBP responses to three tasks were less predictive compared to an individual task (i.e., mental arithmetic). Of importance, hemodynamic reactivity (namely CO and TPR) did not predict future BP suggesting that more general psychophysiological processes (e.g., inflammation, platelet aggregation) may be implicated, or that BP, but not hemodynamic reactivity may be a marker of hypertension.
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http://dx.doi.org/10.1017/sjp.2016.5DOI Listing
March 2016

Seasonal fluxes of carbonyl sulfide in a midlatitude forest.

Proc Natl Acad Sci U S A 2015 Nov 2;112(46):14162-7. Epub 2015 Nov 2.

Harvard School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138; Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138;

Carbonyl sulfide (OCS), the most abundant sulfur gas in the atmosphere, has a summer minimum associated with uptake by vegetation and soils, closely correlated with CO2. We report the first direct measurements to our knowledge of the ecosystem flux of OCS throughout an annual cycle, at a mixed temperate forest. The forest took up OCS during most of the growing season with an overall uptake of 1.36 ± 0.01 mol OCS per ha (43.5 ± 0.5 g S per ha, 95% confidence intervals) for the year. Daytime fluxes accounted for 72% of total uptake. Both soils and incompletely closed stomata in the canopy contributed to nighttime fluxes. Unexpected net OCS emission occurred during the warmest weeks in summer. Many requirements necessary to use fluxes of OCS as a simple estimate of photosynthesis were not met because OCS fluxes did not have a constant relationship with photosynthesis throughout an entire day or over the entire year. However, OCS fluxes provide a direct measure of ecosystem-scale stomatal conductance and mesophyll function, without relying on measures of soil evaporation or leaf temperature, and reveal previously unseen heterogeneity of forest canopy processes. Observations of OCS flux provide powerful, independent means to test and refine land surface and carbon cycle models at the ecosystem scale.
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http://dx.doi.org/10.1073/pnas.1504131112DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4655539PMC
November 2015

Erratum: "Magnetic nanoparticles with high specific absorption rate of electromagnetic energy at low field strength for hyperthermia therapy" [J. Appl. Phys. , 094302 (2015)].

J Appl Phys 2015 Nov 3;118(17):179901. Epub 2015 Nov 3.

School of Engineering at Dartmouth College , 14 Engineering Drive, Hanover, New Hampshire 03755, USA.

[This corrects the article , PMID: 25825545.].
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http://dx.doi.org/10.1063/1.4935331DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4636495PMC
November 2015

The Dartmouth Center for Cancer Nanotechnology Excellence: magnetic hyperthermia.

Nanomedicine (Lond) 2015 ;10(11):1685-92

Thayer School of Engineering, 14 Engineering Drive, Hanover, NH 03755, USA.

The Dartmouth Center for Cancer Nanotechnology Excellence - one of nine funded by the National Cancer Institute as part of the Alliance for Nanotechnology in Cancer - focuses on the use of magnetic nanoparticles for cancer diagnostics and hyperthermia therapy. It brings together a diverse team of engineers and biomedical researchers with expertise in nanomaterials, molecular targeting, advanced biomedical imaging and translational in vivo studies. The goal of successfully treating cancer is being approached by developing nanoparticles, conjugating them with Fabs, hyperthermia treatment, immunotherapy and sensing treatment response.
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http://dx.doi.org/10.2217/nnm.15.64DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4493741PMC
April 2016

Simulations of chlorophyll fluorescence incorporated into the Community Land Model version 4.

Glob Chang Biol 2015 Sep 19;21(9):3469-77. Epub 2015 Jun 19.

Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA, 91109, USA.

Several studies have shown that satellite retrievals of solar-induced chlorophyll fluorescence (SIF) provide useful information on terrestrial photosynthesis or gross primary production (GPP). Here, we have incorporated equations coupling SIF to photosynthesis in a land surface model, the National Center for Atmospheric Research Community Land Model version 4 (NCAR CLM4), and have demonstrated its use as a diagnostic tool for evaluating the calculation of photosynthesis, a key process in a land surface model that strongly influences the carbon, water, and energy cycles. By comparing forward simulations of SIF, essentially as a byproduct of photosynthesis, in CLM4 with observations of actual SIF, it is possible to check whether the model is accurately representing photosynthesis and the processes coupled to it. We provide some background on how SIF is coupled to photosynthesis, describe how SIF was incorporated into CLM4, and demonstrate that our simulated relationship between SIF and GPP values are reasonable when compared with satellite (Greenhouse gases Observing SATellite; GOSAT) and in situ flux-tower measurements. CLM4 overestimates SIF in tropical forests, and we show that this error can be corrected by adjusting the maximum carboxylation rate (Vmax ) specified for tropical forests in CLM4. Our study confirms that SIF has the potential to improve photosynthesis simulation and thereby can play a critical role in improving land surface and carbon cycle models.
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http://dx.doi.org/10.1111/gcb.12948DOI Listing
September 2015

Antibody-mediated targeting of iron oxide nanoparticles to the folate receptor alpha increases tumor cell association in vitro and in vivo.

Int J Nanomedicine 2015 1;10:2595-617. Epub 2015 Apr 1.

Thayer School of Engineering, Dartmouth, Hanover, NH, USA ; Department of Biological Sciences, Dartmouth, Hanover, NH, USA ; Norris Cotton Cancer Center, Lebanon, NH, USA.

Active molecular targeting has become an important aspect of nanoparticle development for oncology indications. Here, we describe molecular targeting of iron oxide nanoparticles (IONPs) to the folate receptor alpha (FOLRα) using an engineered antibody fragment (Ffab). Compared to control nanoparticles targeting the non-relevant botulinum toxin, the Ffab-IONP constructs selectively accumulated on FOLRα-overexpressing cancer cells in vitro, where they exhibited the capacity to internalize into intracellular vesicles. Similarly, Ffab-IONPs homed to FOLRα-positive tumors upon intraperitoneal administration in an orthotopic murine xenograft model of ovarian cancer, whereas negative control particles showed no detectable tumor accumulation. Interestingly, Ffab-IONPs built with custom 120 nm nanoparticles exhibited lower in vitro targeting efficiency when compared to those built with commercially sourced 180 nm nanoparticles. In vivo, however, the two Ffab-IONP platforms achieved equivalent tumor homing, although the smaller 120 nm IONPs were more prone to liver sequestration. Overall, the results show that Ffab-mediated targeting of IONPs yields specific, high-level accumulation within cancer cells, and this fact suggests that Ffab-IONPs could have future utility in ovarian cancer diagnostics and therapy.
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http://dx.doi.org/10.2147/IJN.S79367DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4388088PMC
May 2016

Magnetic nanoparticles with high specific absorption rate of electromagnetic energy at low field strength for hyperthermia therapy.

J Appl Phys 2015 Mar 3;117(9):094302. Epub 2015 Mar 3.

Thayer School of Engineering at Dartmouth College , 14 Engineering Drive, Hanover, New Hampshire 03755, USA.

Magnetic nanoparticles (MNPs), referred to as the Dartmouth MNPs, which exhibit high specific absorption rate at low applied field strength have been developed for hyperthermia therapy applications. The MNPs consist of small (2-5 nm) single crystals of gamma-FeO with saccharide chains implanted in their crystalline structure, forming 20-40 nm flower-like aggregates with a hydrodynamic diameter of 110-120 nm. The MNPs form stable (>12 months) colloidal solutions in water and exhibit no hysteresis under an applied quasistatic magnetic field, and produce a significant amount of heat at field strengths as low as 100 Oe at 99-164 kHz. The MNP heating mechanisms under an alternating magnetic field (AMF) are discussed and analyzed quantitatively based on (a) the calculated multi-scale MNP interactions obtained using a three dimensional numerical model called the method of auxiliary sources, (b) measured MNP frequency spectra, and (c) quantified MNP friction losses based on magneto-viscous theory. The frequency responses and hysteresis curves of the Dartmouth MNPs are measured and compared to the modeled data. The specific absorption rate of the particles is measured at various AMF strengths and frequencies, and compared to commercially available MNPs. The comparisons demonstrate the superior heating properties of the Dartmouth MNPs at low field strengths (<250 Oe). This may extend MNP hyperthermia therapy to deeper tumors that were previously non-viable targets, potentially enabling the treatment of some of the most difficult cancers, such as pancreatic and rectal cancers, without damaging normal tissue.
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http://dx.doi.org/10.1063/1.4907915DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4352167PMC
March 2015

Preface to the 13th Physics and Chemistry of Ice Conference (PCI-2014).

J Phys Chem B 2014 Nov;118(47):13323

Thayer School of Engineering at Dartmouth College.

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http://dx.doi.org/10.1021/jp507860kDOI Listing
November 2014

Self, memory, and imagining the future in a case of psychogenic amnesia.

Neurocase 2015 11;21(6):727-37. Epub 2014 Nov 11.

a Department of Psychology , Oxford Brookes University , Oxford , UK.

We report a case of psychogenic amnesia and examine the relationships between autobiographical memory impairment, the self, and ability to imagine the future. Case study JH, a 60-year-old male, experienced a 6-year period of pervasive psychogenic amnesia covering all life events from childhood to the age of 53. JH was tested during his amnesic period and again following hypnotherapy and the recovery of his memories. JH's amnesia corresponded with deficits in self-knowledge and imagining the future. Results are discussed with reference to models of self and memory and processes involving remembering and imagining.
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http://dx.doi.org/10.1080/13554794.2014.977923DOI Listing
May 2016

Climate change and forest fires synergistically drive widespread melt events of the Greenland Ice Sheet.

Proc Natl Acad Sci U S A 2014 Jun 19;111(22):7964-7. Epub 2014 May 19.

Thayer School of Engineering, Dartmouth College, Hanover, NH 03755; and.

In July 2012, over 97% of the Greenland Ice Sheet experienced surface melt, the first widespread melt during the era of satellite remote sensing. Analysis of six Greenland shallow firn cores from the dry snow region confirms that the most recent prior widespread melt occurred in 1889. A firn core from the center of the ice sheet demonstrated that exceptionally warm temperatures combined with black carbon sediments from Northern Hemisphere forest fires reduced albedo below a critical threshold in the dry snow region, and caused the melting events in both 1889 and 2012. We use these data to project the frequency of widespread melt into the year 2100. Since Arctic temperatures and the frequency of forest fires are both expected to rise with climate change, our results suggest that widespread melt events on the Greenland Ice Sheet may begin to occur almost annually by the end of century. These events are likely to alter the surface mass balance of the ice sheet, leaving the surface susceptible to further melting.
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http://dx.doi.org/10.1073/pnas.1405397111DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4050608PMC
June 2014

A comparison of τ-MnAl particulates produced via different routes.

J Phys Condens Matter 2014 Feb;26(6):064201

MnAl alloys are very promising rare-earth-free permanent magnets. Nanocrystalline microstructures can have beneficial effects on the properties of magnetic MnAl alloys. In the present work we examined multiple routes to process MnAl alloys and studied the effects of milling on Mn-46 at.% Al powders. Mn54Al46 was produced via gas atomization, melt spinning, and rapid solidification rate processing. It was then mechanically milled using a water-cooled Union Process attritor for times up to 20 h. X-ray diffraction patterns showed the presence of mostly the high-temperature ε-phase with significant amounts of the equilibrium γ2 and β phases in both the cast and milled particulates. The powders were annealed for various temperatures and times in order to obtain the ferromagnetic τ-phase. Magnetic measurements of the optimally annealed powders showed a coercivity of 3.62 kOe and saturation magnetization of 59.8 emu g(-1) for mechanically milled gas-atomized powder annealed at 500 °C for 30 min.
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http://dx.doi.org/10.1088/0953-8984/26/6/064201DOI Listing
February 2014

Persistent anterograde amnesia following limbic encephalitis associated with antibodies to the voltage-gated potassium channel complex.

J Neurol Neurosurg Psychiatry 2014 Apr 8;85(4):387-91. Epub 2014 Jan 8.

Nuffield Department of Clinical Neurosciences, John Radcliffe Hospital, , Oxford, UK.

Objective: Limbic encephalitis (LE) associated with antibodies to the voltage-gated potassium channel complex (VGKC) is a potentially reversible cause of cognitive impairment. Despite the prominence of cognitive dysfunction in this syndrome, little is known about patients' neuropsychological profile at presentation or their long-term cognitive outcome.

Methods: We used a comprehensive neuropsychological test battery to evaluate cognitive function longitudinally in 19 patients with VGKC-LE.

Results: Before immunotherapy, the group had significant impairment of memory, processing speed and executive function, whereas language and perceptual organisation were intact. At follow-up, cognitive impairment was restricted to the memory domain, with processing speed and executive function having returned to the normal range. Residual memory function was predicted by the antibody titre at presentation.

Conclusions: The results show that, despite broad cognitive dysfunction in the acute phase, patients with VGKC-LE often make a substantial recovery with immunotherapy but may be left with permanent anterograde amnesia.
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http://dx.doi.org/10.1136/jnnp-2013-306724DOI Listing
April 2014

[Modeling of CO2 fluxes at cropland by using SiB3 model].

Huan Jing Ke Xue 2013 Oct;34(10):4000-8

Department of Atmosphere Science, Colorado State University, CO 80523, USA.

The aim is to study the influence of different vegetation types on CO2 fluxes at the same site, taking farmland as the object by using the simple biosphere model (SiB3) , select different vegetation types in Suzhou Dongshan site as input parameters of model to simulate CO2 fluxes, and compare with the observational data in Suzhou Dongshan site during 2011-04-16 to 2011-06-30. Results show that using corn as the site vegetation type input model to simulate CO2 fluxes showed a very good diurnal variation agreement compared to the measured data, but selecting the ordinary crop type input model to simulate CO2 fluxes, CO2 fluxes during the daytime in April and May were undervalued, and CO2 fluxes in June were overvalued; when we select the tea type to input the model, the simulated results significantly overestimated CO2 fluxes during the daytime in May and June. In addition, when using SiB3 model to simulate the daily CO2 fluxes, all three vegetation types input model can effectively simulate daily CO2 fluxes, but not significantly. It shows that choosing the right type vegetation input SiB3 model can effectively simulate the diurnal variation of CO2 fluxes, but can not effectively improve the daily CO2 fluxes simulation.
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October 2013

Deep brain stimulation of the anterior cingulate cortex: targeting the affective component of chronic pain.

Neuroreport 2014 Jan;25(2):83-8

aOxford Functional Neurosurgery and Experimental Neurology Group, Nuffield Departments of Clinical Neuroscience and Surgery bDepartment of Psychiatry, University of Oxford cRussell Cairn Unit, West Wing, John Radcliffe Hospital, Oxford, UK.

Deep brain stimulation (DBS) has shown promise for relieving nociceptive and neuropathic symptoms of refractory chronic pain. We assessed the efficacy of a new target for the affective component of pain, the anterior cingulate cortex (ACC). A 49-year-old man with neuropathic pain underwent bilateral ACC DBS. Patient-reported outcome measures were collected before and 2 years after surgery using a Visual Analogue Scale, Short-Form 36 quality of life survey, McGill pain questionnaire, EuroQol-5D questionnaires (EQ-5D; Health State) and neuropsychological assessments. The patient improved with DBS. Two years after surgery, the Visual Analogue Scale decreased from 6.7 to 3.0, McGill pain questionnaire improved by 42% and EQ-5D Health State increased by 150%. Stimulating the ACC at 130 Hz, 330 µs and 3 V facilitated neuropathic pain relief. The DBS remained efficacious during the 2-year follow-up period. Affective ACC DBS can relieve chronic neuropathic pain refractory to pharmacotherapy and restore quality of life.
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http://dx.doi.org/10.1097/WNR.0000000000000039DOI Listing
January 2014

Understanding mNP Hyperthermia for cancer treatment at the cellular scale.

Proc SPIE Int Soc Opt Eng 2013 Feb;8584:85840E

Thayer School of Engineering, Dartmouth College, Hanover NH 03755 USA ; Dartmouth Medical School, Hanover NH 03755 USA.

The use of magnetic nanoparticles (mNP's) to induce local hyperthermia has been emerging in recent years as a promising cancer therapy, in both a stand-alone and combination treatment setting. Studies have shown that cancer cells associate with, internalize, and aggregate mNP's more preferentially than normal cells. Once the mNP's are delivered inside the cells, a low frequency (30 kHz-300 kHz) alternating electromagnetic field is used to activate the mNP's. The nanoparticles absorb the applied field and provide localized heat generation at nano-micron scales. It has been shown experimentally that mNP's exhibit collective behavior when in close proximity. Although most prevailing mNP heating models assume there is no magnetic interaction between particles, our data suggests that magnetic interaction effects due to mNP aggregation are often significant; In the case of multi-crystal core particles, interaction is guaranteed. To understand the physical phenomena responsible for this effect, we modeled electromagnetic coupling between mNP's in detail. The computational results are validated using data from the literature as well as measurements obtained in our lab. The computational model presented here is based on a method of moments technique and is used to calculate magnetic field distributions on the nanometer scale, both inside and outside the mNP.
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http://dx.doi.org/10.1117/12.2007518DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4169898PMC
February 2013