Publications by authors named "Tianmin Liu"

14 Publications

  • Page 1 of 1

Femtosecond X-ray induced changes of the electronic and magnetic response of solids from electron redistribution.

Nat Commun 2019 11 21;10(1):5289. Epub 2019 Nov 21.

SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA, 94025, USA.

Resonant X-ray absorption, where an X-ray photon excites a core electron into an unoccupied valence state, is an essential process in many standard X-ray spectroscopies. With increasing X-ray intensity, the X-ray absorption strength is expected to become nonlinear. Here, we report the onset of such a nonlinearity in the resonant X-ray absorption of magnetic Co/Pd multilayers near the Co L[Formula: see text] edge. The nonlinearity is directly observed through the change of the absorption spectrum, which is modified in less than 40 fs within 2 eV of its threshold. This is interpreted as a redistribution of valence electrons near the Fermi level. For our magnetic sample this also involves mixing of majority and minority spins, due to sample demagnetization. Our findings reveal that nonlinear X-ray responses of materials may already occur at relatively low intensities, where the macroscopic sample is not destroyed, providing insight into ultrafast charge and spin dynamics.
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http://dx.doi.org/10.1038/s41467-019-13272-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6872582PMC
November 2019

Magnetic Switching in Granular FePt Layers Promoted by Near-Field Laser Enhancement.

Nano Lett 2017 04 17;17(4):2426-2432. Epub 2017 Mar 17.

Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory , 2575 Sand Hill Road, Menlo Park, California 94025, United States.

Light-matter interaction at the nanoscale in magnetic materials is a topic of intense research in view of potential applications in next-generation high-density magnetic recording. Laser-assisted switching provides a pathway for overcoming the material constraints of high-anisotropy and high-packing density media, though much about the dynamics of the switching process remains unexplored. We use ultrafast small-angle X-ray scattering at an X-ray free-electron laser to probe the magnetic switching dynamics of FePt nanoparticles embedded in a carbon matrix following excitation by an optical femtosecond laser pulse. We observe that the combination of laser excitation and applied static magnetic field, 1 order of magnitude smaller than the coercive field, can overcome the magnetic anisotropy barrier between "up" and "down" magnetization, enabling magnetization switching. This magnetic switching is found to be inhomogeneous throughout the material with some individual FePt nanoparticles neither switching nor demagnetizing. The origin of this behavior is identified as the near-field modification of the incident laser radiation around FePt nanoparticles. The fraction of not-switching nanoparticles is influenced by the heat flow between FePt and a heat-sink layer.
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http://dx.doi.org/10.1021/acs.nanolett.7b00052DOI Listing
April 2017

Plasma miR-10a: A Potential Biomarker for Coronary Artery Disease.

Dis Markers 2016 22;2016:3841927. Epub 2016 May 22.

Department of Cardiology, The Fifth Affiliated Hospital of Sun Yat-sen University, Zhuhai, Guangdong 519000, China.

Aims. MicroRNAs (miRNAs) are involved in the pathogenesis of coronary artery disease (CAD). The objective of this study is to determine plasma levels of miR-10a in CAD and analyze its association with the severity of CAD. Materials and Methods. Plasma miR-10a levels in 60 CAD patients including stable angina pectoris (SAP) (n = 29), unstable angina pectoris (UAP) or non-ST elevation myocardial infarction (MI) (NSTEMI) (n = 17), or ST elevation MI (STEMI) (n = 14) and 20 non-CAD subjects were assessed by real-time polymerase chain reaction (qRT-PCR), and associations of miR-10a levels with risk factors of CAD and its severity were analyzed. Results. The qRT-PCR results showed that plasma miR-10a levels were decreased in CAD patients, and CAD with high SYNTAX scores or STEMI was significantly associated with lower miR-10a levels. Conclusions. Lower plasma miR-10a levels were negatively associated with the presence as well as severity of CAD, and plasma miR-10a can act as a potential biomarker for estimating the presence and severity of CAD.
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http://dx.doi.org/10.1155/2016/3841927DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4893451PMC
February 2017

Femtosecond X-ray magnetic circular dichroism absorption spectroscopy at an X-ray free electron laser.

Rev Sci Instrum 2016 Mar;87(3):033110

SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA.

X-ray magnetic circular dichroism spectroscopy using an X-ray free electron laser is demonstrated with spectra over the Fe L(3,2)-edges. The high brightness of the X-ray free electron laser combined with high accuracy detection of incident and transmitted X-rays enables ultrafast X-ray magnetic circular dichroism studies of unprecedented sensitivity. This new capability is applied to a study of all-optical magnetic switching dynamics of Fe and Gd magnetic sublattices in a GdFeCo thin film above its magnetization compensation temperature.
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http://dx.doi.org/10.1063/1.4944410DOI Listing
March 2016

Cerebrospinal fluid neuropeptide Y-like immunoreactivity correlates with impulsive aggression in human subjects.

Biol Psychiatry 2012 Dec 15;72(12):997-1003. Epub 2012 Sep 15.

Department of Psychiatry and Behavioral Neuroscience, Clinical Neuroscience Research Unit, Pritzker School of Medicine, The University of Chicago, Chicago, IL 60637, USA.

Background: Neurochemical studies have pointed to a modulatory role in human aggression for a number of central neurotransmitters; some (e.g., serotonin) appear to play an inhibitory role, while others (e.g., vasopressin) appear to play a facilitator role in the modulation of aggression. While recent animal studies of neuropeptide Y (NPY) have suggested a facilitator role for central NPY in the modulation of aggression, no human studies of central NPY have yet been reported regarding aggression.

Methods: Basal lumbar cerebrospinal fluid (CSF) was obtained from 60 physically healthy subjects with personality disorder (PD) (n=40) and from healthy volunteers (n=20). These samples were then assessed for CSF NPY-like immunoreactivity (NPY-LI) and other neurotransmitter-related species in CSF and correlated with measures of aggression and impulsivity.

Results: Cerebrospinal fluid NPY-LI was higher in PD subjects compared with healthy volunteers and in subjects with intermittent explosive disorder compared with those without intermittent explosive disorder. In PD subjects, CSF NPY-LI was directly correlated with composite measures of aggression and impulsivity and a composite measure of impulsive aggression. Group differences in CSF NPY-LI concentration were accounted for by measures of impulsive aggression.

Conclusions: These data suggest a direct relationship between CSF NPY-immunoreactivity concentration and measures of impulsive aggression in human subjects. This adds to the complex picture of the central neuromodulatory role of impulsive aggression in human subjects.
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http://dx.doi.org/10.1016/j.biopsych.2012.07.029DOI Listing
December 2012

Quetiapine affects neuropeptide Y and corticotropin-releasing hormone in cerebrospinal fluid from schizophrenia patients: relationship to depression and anxiety symptoms and to treatment response.

Int J Neuropsychopharmacol 2012 Sep 19;15(8):1051-61. Epub 2011 Oct 19.

Department of Psychiatry and Psychotherapy, Klinikum Fulda gAG, Fulda, Germany.

Cumulative evidence indicates that neuropeptides play a role in the pathophysiology of schizophrenia. Early data showed increased neuropeptide Y (NPY) in cerebrospinal fluid (CSF) from schizophrenia patients and data from rodents show that antipsychotic drugs modulate NPY levels in and release from selected rat brain regions. In view of these findings we investigated whether the atypical antipsychotic quetiapine, originally used as an antipsychotic but subsequently shown to be efficient also in major depressive disorder and in both poles of bipolar disorder, would affect NPY-like immunoreactivity (-LI), and corticotropin-releasing hormone (CRH)-LI levels in CSF of schizophrenia patients. NPY-LI and CRH-LI in CSF were determined in 22 patients with schizophrenia. Lumbar puncture was performed at baseline and again after 4 wk of quetiapine treatment (600 mg/d). Patients were assessed with the Positive and Negative Syndrome Scale (PANSS) at baseline and at weekly intervals. Quetiapine treatment was associated with a significant increase in NPY-LI (p<0.001) and decrease in CRH-LI (p<0.01). Stepwise multiple regression analysis revealed that ΔNPY-LI and ΔCRH-LI levels predicted 63% (p<0.001) of the variability of the ΔPANSS total score, ΔNPY-LI 42% (p<0.05) of the ΔPANSS anxiety items (G2) and ΔCRH-LI 40% (p=0.05) of the ΔPANSS depression items (G6). These results suggest that while quetiapine's effects on monoamines are probably related to its antipsychotic properties, the modulation of NPY and CRH accounts for its antidepressant and anxiolytic effects and can be markers of response.
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http://dx.doi.org/10.1017/S1461145711001556DOI Listing
September 2012

The neuropeptide Y (NPY)-ergic system is associated with behavioral resilience to stress exposure in an animal model of post-traumatic stress disorder.

Neuropsychopharmacology 2012 Jan 5;37(2):350-63. Epub 2011 Oct 5.

Anxiety and Stress Research Unit, Beer-Sheva Mental Health Center, The State of Israel Ministry of Health, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel.

Converging evidence implicates the regulatory neuropeptide Y (NPY) in anxiety- and depression-related behaviors. The present study sought to assess whether there is an association between the magnitude of behavioral responses to stress and patterns of NPY in selected brain areas, and subsequently, whether pharmacological manipulations of NPY levels affect behavior in an animal model of PTSD. Animals were exposed to predator-scent stress for 15 min. Behaviors were assessed with the elevated plus maze and acoustic startle response tests 7 days later. Preset cutoff criteria classified exposed animals according to their individual behavioral responses. NPY protein levels were assessed in specific brain regions 8 days after the exposure. The behavioral effects of NPY agonist, NPY-Y1-receptor antagonist, or placebo administered centrally 1 h post-exposure were evaluated in the same manner. Immunohistochemical technique was used to detect the expression of the NPY, NPY-Y1 receptor, brain-derived neurotrophic factor, and GR 1 day after the behavioral tests. Animals whose behavior was extremely disrupted (EBR) selectively displayed significant downregulation of NPY in the hippocampus, periaqueductal gray, and amygdala, compared with animals whose behavior was minimally (MBR) or partially (PBR) disrupted, and with unexposed controls. One-hour post-exposure treatment with NPY significantly reduced prevalence rates of EBR and reduced trauma-cue freezing responses, compared with vehicle controls. The distinctive pattern of NPY downregulation that correlated with EBR as well as the resounding behavioral effects of pharmacological manipulation of NPY indicates an intimate association between NPY and behavioral responses to stress, and potentially between molecular and psychopathological processes, which underlie the observed changes in behavior. The protective qualities attributed to NPY are supported by the extreme reduction of its expression in animals severely affected by the stressor and imply a role in promoting resilience and/or recovery.
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http://dx.doi.org/10.1038/npp.2011.230DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3242318PMC
January 2012

The neuroendocrinology of childhood trauma in personality disorder.

Psychoneuroendocrinology 2012 Jan 8;37(1):78-86. Epub 2011 Jun 8.

The University of Chicago Medical Center, 5841 S. Maryland Ave, Chicago, IL 60637, USA.

Background: Childhood trauma has been associated with elevated central corticotropin releasing hormone (CRH) drive in adults meeting general DSM-IV criteria for personality disorder. It is not clear how this may be related to pituitary or adrenal responsiveness in personality disorder. It was hypothesized that high levels of childhood trauma would be associated with blunted cortisol and adrenocorticotropin releasing hormone (ACTH) response to the combined dexamethasone(DEX)/CRH test in adults meeting general DSM-IV criteria for personality disorder.

Method: 24 healthy, medication free adults with personality disorder (N=16) and a group of healthy controls (N=8) underwent semi-structured diagnostic interviews and completed the Childhood Trauma Questionnaire (CTQ). Across two separate study sessions separated by at least a week, cerebrospinal fluid (CSF) was sampled by lumbar puncture for measurement of CRH concentration (N=17), and peripheral blood cortisol and ACTH levels were measured after challenge with DEX/CRH (N=24).

Results: As hypothesized, high CTQ score was associated with a blunted cortisol and ACTH response to DEX/CRH challenge. Indices of cortisol and ACTH response (peak level and area under the curve (AUC)) to DEX/CRH were in turn significantly negatively correlated with CSF CRH concentration.

Conclusion: Childhood trauma in adults with personality disorder is associated with blunted cortisol and ACTH secretion following DEX/CRH challenge. These effects are independent of depression or posttraumatic stress disorder. Previous work would suggest that blunted pituitary-adrenal response is related to elevated central CRH drive. Corroborating this, CSF CRH levels were significantly and negatively correlated with peak level and AUC of both cortisol and ACTH.
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http://dx.doi.org/10.1016/j.psyneuen.2011.05.006DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3178739PMC
January 2012

Prolonged chronic ethanol exposure alters neuropeptide Y and corticotropin-releasing factor levels in the brain of adult Wistar rats.

Pharmacol Biochem Behav 2011 Jul 17;99(1):104-11. Epub 2011 Apr 17.

Molecular and Integrative Neurosciences Department, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA.

There is evidence to suggest that alterations in neuropeptide Y (NPY) and corticotropin-releasing factor (CRF) contribute to the escalated voluntary ethanol intake seen following long term chronic ethanol exposure. The present study assessed whether the duration of chronic ethanol exposure and abstinence alters brain levels of NPY and CRF in adult Wistar rats. NPY-like immunoreactivity (NPY-LI) and CRF-LI were determined in the amygdala (AMYG), frontal cortex (FCTX), hippocampus (HPC) and parietal cortex (PCTX) of adult Wistar rats after chronic ethanol exposure, and 24-h and 2-weeks following withdrawal (WD). Chronic ethanol exposure consisted of either a 2-week or an 8-week ethanol vapor regimen. No change in brain levels of NPY-LI, CRF-LI and the NPY-LI/CRF-LI ratio was observed 2-weeks following ethanol exposure, whereas, 8-weeks of ethanol exposure produced a significant effect on NPY-LI expression in the AMYG and FCTX. Moreover, an 8-week ethanol vapor regimen significantly increased CRF-LI levels in the HPC and PCTX. Findings from the present study suggest that a longer duration of ethanol vapor, similar to what is required to enhance voluntary drinking, is required to produce changes in NPY-LI and CRF-LI expression in the adult rat brain.
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http://dx.doi.org/10.1016/j.pbb.2011.04.005DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3120013PMC
July 2011

Effects of prolonged ethanol vapor exposure on forced swim behavior, and neuropeptide Y and corticotropin-releasing factor levels in rat brains.

Alcohol 2010 Sep 12;44(6):487-93. Epub 2010 Aug 12.

Molecular and Integrative Neurosciences Department, The Scripps Research Institute, La Jolla, CA, USA.

Depressive symptoms in alcohol-dependent individuals are well-recognized and clinically relevant phenomena. The etiology has not been elucidated although it is clear that the depressive symptoms may be alcohol independent or alcohol induced. To contribute to the understanding of the neurobiology of chronic ethanol use, we investigated the effects of chronic intermittent ethanol vapor exposure on behaviors in the forced swim test (FST) and neuropeptide Y (NPY) and corticotropin-releasing factor (CRF) levels in specific brain regions. Adult male Wistar rats were subjected to intermittent ethanol vapor (14 h on/10 h off) or air exposure for 2 weeks and were then tested at three time points corresponding to acute withdrawal (8-12 h into withdrawal) and protracted withdrawal (30 and 60 days of withdrawal) in the FST. The behaviors that were measured in the five-min FST consisted of latency to immobility, swim time, immobility time, and climbing time. The FST results showed that the vapor-exposed animals displayed depressive-like behaviors; for instance, decreased latency to immobility in acute withdrawal and decreased latency to immobility, decreased swim time and increased immobility time in protracted withdrawal, with differences between air- and vapor-exposed animals becoming more pronounced over the 60-day withdrawal period. NPY levels in the frontal cortex of the vapor-exposed animals were decreased compared with the control animals, and CRF levels in the amygdala were correlated with increased immobility time. Thus, extended ethanol vapor exposure produced long-lasting changes in FST behavior and NPY levels in the brain.
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http://dx.doi.org/10.1016/j.alcohol.2010.06.006DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2954060PMC
September 2010

Preclinical studies of carbohydrate mimetic peptide vaccines for breast cancer and melanoma.

Vaccine 2007 Apr 26;25(16):3022-31. Epub 2007 Jan 26.

Arkansas Cancer Research Center, Department of Pathology, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA.

Limited immune responses to tumor-associated carbohydrate antigens (TACA) are due in part to their being self-antigens. Immunization with xenoantigens of TACA provides an approach to break tolerance and augment responses to TACA. Carbohydrate mimetic peptides (CMPs) as xenoantigens can induce serum antibodies that target shared carbohydrate residues on differing carbohydrate structures. In preclinical studies, we observe that CMP immunization in mice induce immune responses that are effective in inhibiting the in vitro and in vivo growth of breast cancer and melanoma tumor cells expressing self-target antigens. CMPs of TACA can be further defined that induce IgM antibodies with broadened responses to both breast and melanoma cells. Consequently, CMPs are effective at generating a multifaceted carbohydrate-reactive immune response that should be clinically evaluated for their ability to amplify carbohydrate immune responses against circulating or disseminated tumor cells.
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http://dx.doi.org/10.1016/j.vaccine.2007.01.072DOI Listing
April 2007

Significance of the detection of HIV-1 gag- and/or pol-CD8/A2 T-lymphocytes in HIV-patients.

Immunol Lett 2005 Apr 25;98(1):73-81. Epub 2004 Nov 25.

RDL Reference Laboratory, 10755 Venice Blvd, Los Angeles, CA 90034, USA.

Unlabelled: Cytotoxic T-lymphocytes (CTL) play an important role in the immune system's defense against human immunodeficiency virus (HIV) infection. The functional status of CTL closely relates to the progression of HIV disease. We have validated the characteristics of the assay for HIV-1 gag- and pol-specific-CD8/HLA-A2 T-cells from peripheral blood by flow cytometry. Sixty-nine healthy individuals and 38 HIV-patients with HLA-A2 antigen-positive subjects were included in the study. Neither HIV-1 gag- nor pol-specific-CD8/HLA-A2 T-cells were determined in these healthy subjects. HIV-1 gag- and pol-specific-CD8/HLA-A2 T-cells could be detected in HIV-patients. The frequency of specific CTL was 58% (22/38) in the patient group. There was a significantly inverse correlation (p < 0.05) between HIV-1 gag- and pol-specific-CD8/HLA-A2 T-cells and HIV plasma viremia in the patients.

Conclusion: The HIV-1 gag- or pol-specific-CD8/HLA-A2 T-cells assay is sensitive and specific, being able to detect at the single T-cell level. This assay may provide a versatile tool for structured HIV treatment and for monitoring vaccination efficacy.
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http://dx.doi.org/10.1016/j.imlet.2004.10.016DOI Listing
April 2005

Bioengineering of surface GD3 ganglioside for immunotargeting human melanoma cells.

J Biol Chem 2004 Jun 26;279(24):25390-9. Epub 2004 Mar 26.

Institute for Biological Sciences, National Research Council of Canada, Ottawa, Ontario K1A 0R6, Canada.

N-Propionyl, N-butyryl (N-Bu), and N-benzoyl mannosamine, as precursors of sialic acid biosynthesis, were incubated with human melanoma SK-MEL-28 cells and resulted in the replacement of N-acetyl groups on the cell surface sialic acid residues, including those associated with GD3. Meanwhile, vaccines containing GD3 and modified GD3 tetrasaccharide-keyhole limpet hemocyanin conjugates were synthesized, and BALB/c mice were immunized with them together with monophosphoryl lipid A adjuvant. The GD3Bu-keyhole limpet hemocyanin conjugate raised the highest IgG titers without any cross-reactivity to unmodified GD3. Expression of GD3Bu epitopes on the surface of SK-MEL-28 cells was confirmed in vitro and in vivo by the binding of a polyclonal antiserum and monoclonal antibody (mAb) 2A, both of which specifically recognize GD3Bu, and by mass spectroscopic analysis of glycolipids extracted from cells. Following expression of GD3Bu on the surface of SK-MEL-28 cells, the cells could be lysed by mAb 2A and GD3Bu antiserum in the presence of complement. Although less effective in the control of existing large size tumors ( approximately 10 mm inner diameter) on BALB/c nu/nu mice, mAb 2A in combination with ManNBu effectively protected mice from SK-MEL-28 tumor grafting. This approach may provide a method to augment the immunogenicity of sialylated human antigens and to avoid generating an autoimmune response to them at same time.
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http://dx.doi.org/10.1074/jbc.M402787200DOI Listing
June 2004
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