Publications by authors named "Kamal P Singh"

13 Publications

  • Page 1 of 1

Universal Stokes's nanomechanical viscometer.

Sci Rep 2021 Jul 13;11(1):14365. Epub 2021 Jul 13.

Department of Physical Sciences, Indian Institute of Science Education and Research, Mohali, Knowledge City, Sector 81, Manauli, 140306, India.

Although, many conventional approaches have been used to measure viscosity of fluids, most methods do not allow non-contact, rapid measurements on small sample volume and have universal applicability to all fluids. Here, we demonstrate a simple yet universal viscometer, as proposed by Stokes more than a century ago, exploiting damping of capillary waves generated electrically and probed optically with sub-nanoscale precision. Using a low electric field local actuation of fluids we generate quasi-monochromatic propagating capillary waves and employ a pair of single-lens based compact interferometers to measure attenuation of capillary waves in real-time. Our setup allows rapid measurement of viscosity of a wide variety of polar, non-polar, transparent, opaque, thin or thick fluids having viscosity values varying over four orders of magnitude from [Formula: see text]. Furthermore, we discuss two additional damping mechanisms for nanomechanical capillary waves caused by bottom friction and top nano-layer appearing in micro-litre droplets. Such self-stabilized droplets when coupled with precision interferometers form interesting microscopic platform for picomechanical optofluidics for fundamental, industrial and medical applications.
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http://dx.doi.org/10.1038/s41598-021-93729-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8277784PMC
July 2021

Optimal Protein Sequence Design Mitigates Mechanical Failure in Silk β-Sheet Nanocrystals.

ACS Biomater Sci Eng 2021 Jul 21;7(7):3156-3165. Epub 2021 Jun 21.

Department of Biological Sciences, Indian Institute of Science Education and Research Mohali, Sector 81, Knowledge City, Manauli PO, SAS Nagar 140306, India.

The excellent mechanical strength and toughness of spider silk are well characterized experimentally and understood atomistically using computational simulations. However, little attention has been focused on understanding whether the amino acid sequence of β-sheet nanocrystals, which is the key to rendering strength to silk fiber, is optimally chosen to mitigate molecular-scale failure mechanisms. To investigate this, we modeled β-sheet nanocrystals of various representative small/polar/hydrophobic amino acid repeats for determining the sequence motif having superior nanomechanical tensile strength and toughness. The constant velocity pulling of the central β-strand in the nanocrystal, using steered molecular dynamics, showed that homopolymers of small amino acid (alanine/alanine-glycine) sequence motifs, occurring in natural silk fibroin, have better nanomechanical properties than other modeled structures. Further, we analyzed the hydrogen bond (HB) and β-strand pull dynamics of modeled nanocrystals to understand the variation in their rupture mechanisms and explore sequence-dependent mitigating factors contributing to their superior mechanical properties. Surprisingly, the enhanced side-chain interactions in homopoly-polar/hydrophobic amino acid models are unable to augment backbone HB cooperativity to increase mechanical strength. Our analyses suggest that nanocrystals of pristine silk sequences most likely achieve superior mechanical strength by optimizing side-chain interaction, packing, and main-chain HB interactions. Thus, this study suggests that the nanocrystal β-sheet sequence plays a crucial role in determining the nanomechanical properties of silk, and the evolutionary process has optimized it in natural silk. This study provides insight into the molecular design principle of silk with implications in the genetically modified artificial synthesis of silk-like biomaterials.
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http://dx.doi.org/10.1021/acsbiomaterials.1c00447DOI Listing
July 2021

In-line ultra-thin attosecond delay line with direct absolute-zero delay reference and high stability.

Opt Lett 2020 Sep;45(18):5266-5269

We introduce an ultra-thin attosecond optical delay line based on controlled wavefront division of a femtosecond infrared pulse after transmission through a pair of micrometer-thin glass plates with negligible dispersion effects. The time delay between the two pulses is controlled by rotating one of the glass plates from absolute zero to several optical cycles, with 2.5 as to tens of attosecond resolution with 2 as stability, as determined by interferometric self-calibration. The performance of the delay line is validated by observing attosecond-resolved oscillations in the yield of high harmonics induced by time delayed infrared pulses, in agreement with a numerical simulation for a simple model atom. This approach can be extended in the future for performing XUV-IR attosecond pump-probe experiments.
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http://dx.doi.org/10.1364/OL.403842DOI Listing
September 2020

Time-resolved nano-Newton force spectroscopy in air and vacuum using a load cell of ultra micro-balance.

Rev Sci Instrum 2019 Apr;90(4):043117

Department of Physical Sciences, Indian Institute of Science Education and Research Mohali, Sector-81, Manauli 140306, India.

We demonstrate a simple and versatile nanomechanical force measuring setup with 1 nN precision in air and vacuum using a load cell of an ultra-microbalance. We validate stability, precision, and linearity of the load cell with simple tests. The setup is customized to measure stress-strain response of biomaterials (silk, leaf, and flower) and capillary force in fluids. We isolated an optical pull force induced by a Watt-level laser reflected from a mirror/solid surface in air, in addition to optical push force. Furthermore, we add an interferometric probe to directly measure nanoscale deflection of cantilever of the load cell in real-time, thus bypassing its conventional electromagnetic readout, to improve speed and precision of the instrument. We demonstrate nanomechanical force measurement in high vacuum with the same precision and employ radiation pressure to calibrate the load cell for various precision measurements.
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http://dx.doi.org/10.1063/1.5086260DOI Listing
April 2019

The processing and heterostructuring of silk with light.

Nat Mater 2017 09 14;16(9):938-945. Epub 2017 Aug 14.

Department of Physical Sciences, Indian Institute of Science Education and Research Mohali, Sector 81, Knowledge City, Manauli 140306, India.

Spider silk is a tough, elastic and lightweight biomaterial, although there is a lack of tools available for non-invasive processing of silk structures. Here we show that nonlinear multiphoton interactions of silk with few-cycle femtosecond pulses allow the processing and heterostructuring of the material in ambient air. Two qualitatively different responses, bulging by multiphoton absorption and plasma-assisted ablation, are observed for low- and high-peak intensities, respectively. Plasma ablation allows us to make localized nanocuts, microrods, nanotips and periodic patterns with minimal damage while preserving molecular structure. The bulging regime facilitates confined bending and microwelding of silk with materials such as metal, glass and Kevlar with strengths comparable to pristine silk. Moreover, analysis of Raman bands of microwelded joints reveals that the polypeptide backbone remains intact while perturbing its weak hydrogen bonds. Using this approach, we fabricate silk-based functional topological microstructures, such as Mobiüs strips, chiral helices and silk-based sensors.
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http://dx.doi.org/10.1038/nmat4942DOI Listing
September 2017

Nanomechanical effects of light unveil photons momentum in medium.

Sci Rep 2017 02 15;7:42554. Epub 2017 Feb 15.

Department of Physical Sciences, Indian Institute of Science Education and Research Mohali, Sector-81, Manauli 140306, India.

Precision measurement on momentum transfer between light and fluid interface has many implications including resolving the intriguing nature of photons momentum in a medium. For example, the existence of Abraham pressure of light under specific experimental configuration and the predictions of Chau-Amperian formalism of optical momentum for TE and TM polarizations remain untested. Here, we quantitatively and cleanly measure nanomehanical dynamics of water surface excited by radiation pressure of a laser beam. We systematically scanned wide range of experimental parameters including long exposure times, angle of incidence, spot size and laser polarization, and used two independent pump-probe techniques to validate a nano- bump on the water surface under all the tested conditions, in quantitative agreement with the Minkowski's momentum of light. With careful experiments, we demonstrate advantages and limitations of nanometer resolved optical probing techniques and narrow down actual manifestation of optical momentum in a medium.
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http://dx.doi.org/10.1038/srep42554DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5309822PMC
February 2017

Universal Long-Range Nanometric Bending of Water by Light.

Phys Rev Lett 2015 Oct 2;115(14):143902. Epub 2015 Oct 2.

Department of Physical Sciences, Indian Institute of Science Education and Research Mohali, Sector-81, Manauli 140306, India.

Resolving mechanical effects of light on fluids has fundamental importance with wide applications. Most experiments to date on optofluidic interface deformation exploited radiation forces exerted by normally incident lasers. However, the intriguing effects of photon momentum for any configuration, including the unique total internal reflection regime, where an evanescent wave leaks above the interface, remain largely unexplored. A major difficulty in resolving nanomechanical effects has been the lack of a sensitive detection technique. Here, we devise a simple setup whereby a probe laser produces high-contrast Newton-ring-like fringes from a sessile water drop. The mechanical action of the photon momentum of a pump beam modulates the fringes, thus allowing us to perform a direct noninvasive measurement of a nanometric bulge with sub-5-nm precision. Remarkably, a <10  nm difference in the height of the bulge due to different laser polarizations and nonlinear enhancement in the bulge near total internal reflection is isolated. In addition, the nanometric bulge is shown to extend far longer, 100 times beyond the pump spot. Our high precision data validate the century-old Minkowski theory for a general angle and offer potential for novel optofluidic devices and noncontact nanomanipulation strategies.
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http://dx.doi.org/10.1103/PhysRevLett.115.143902DOI Listing
October 2015

Nutrition among men and household food security in an internally displaced persons camp in Kenya.

Public Health Nutr 2016 Mar 28;19(4):723-31. Epub 2015 Apr 28.

School of Public Health and Community Medicine,University of New South Wales,Sydney,NSW 2052,Australia.

Objective: To determine the nutritional status of men and the food security status of their households in an internally displaced persons (IDP) camp in Kenya.

Design: A descriptive, cross-sectional study using a questionnaire and biometric measurements was completed in June 2013.

Setting: IDP camp, Rongai, Kenya.

Subjects: A total of 267 men aged ≥18 years residing within the camp were recruited via respondent-driven sampling. Statistical associations between categorical variables were analysed using Pearson's χ 2 tests, while independent t tests were used for continuous variables.

Results: Among the men surveyed, we found a mean BMI of 20·3 (sd 2·5) kg/m2, with 23·9% of participants in the underweight category (BMI<18·5 kg/m2). The mean Individual Dietary Diversity Score was 6 out of a maximum score of 9. The mean Household Food Insecurity Access Scale score was 11·6 (sd 6·8), with 180 participants (71·7%) residing in households categorised as severely food insecure. Low monthly household income (<2000 Kenyan Shillings, or $US 25) was associated with a higher food insecurity score (P<0·001), greater likelihood of residing in a severely food-insecure household (P<0·001), low dietary diversity score (P<0·05) and being underweight (P<0·01).

Conclusions: While the nutritional status of men in the IDP camp is comparable to non-displaced men in Kenya, household food insecurity is relatively high. Efforts to improve food security for the future are essential to minimise the impact of severe food insecurity on mental health, disease profiles and family well-being reported in other IDP settings.
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http://dx.doi.org/10.1017/S1368980015001275DOI Listing
March 2016

Metformin for the management of gestational diabetes mellitus.

Aust N Z J Obstet Gynaecol 2015 Aug 22;55(4):303-8. Epub 2015 Apr 22.

Liverpool Hospital, Sydney, New South Wales, Australia.

Introduction: Glycaemic control in women with gestational diabetes mellitus (GDM) has typically been achieved with diet, exercise and insulin therapy. Controversy exists in the literature about a potential role for metformin.

Methods: A literature review was completed aiming to compare the glycaemic control, maternal and fetal out comes of metformin therapy with insulin. Searches were completed on databases, including Medline, PubMed and ScienceDirect. Seven randomised control trials (RCTs) fit the inclusion criteria, with a total sample size of 1514 women.

Results: The majority of studies found no difference in glycaemic control between metformin and insulin groups. When comparing maternal outcomes, those receiving metformin therapy recorded less maternal weight gain in four studies. A number of studies reported lower rates of neonatal hypoglycaemia, and one reported higher rates of preterm birth in the metformin group. There were no other differences in the recorded maternal and fetal outcomes.

Discussion: The Jadad score for assessing risk of bias for most included studies was either 3 or 4. The criteria for diagnosis of GDM, maternal and neonatal complications varied between studies. Only one study has published follow-up data, and most are single-centre trials with relatively small sample sizes.

Conclusion: Though there is a growing body of evidence to suggest a role for metformin in GDM management, further large-scale, multicentre RCTs are needed before guidelines can be altered.
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http://dx.doi.org/10.1111/ajo.12311DOI Listing
August 2015

Comment on "low-power laser deformation of an air-liquid interface".

Phys Rev Lett 2013 Feb 12;110(7):079401. Epub 2013 Feb 12.

IISER Mohali, Sector 81, Manauli 140306, India.

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http://dx.doi.org/10.1103/PhysRevLett.110.079401DOI Listing
February 2013

Enhancement of "logical" responses by noise in a bistable optical system.

Phys Rev E Stat Nonlin Soft Matter Phys 2011 Apr 25;83(4 Pt 2):046219. Epub 2011 Apr 25.

Indian Institute of Science Education and Research Mohali, Transit Campus: MGSIPAP Complex, Sector 26, Chandigarh 160019, India.

We verify numerically the phenomenon of logical stochastic resonance in a polarization bistable laser. Namely, we show that when one presents two weak binary inputs to the laser system, the response mirrors a logical OR(NOR) output. The reliability of the logic operation is dependent on the noise intensity. As one increases the noise, the probability of the output reflecting the desired OR(NOR) operation increases to nearly unity and then decreases. We also demonstrate that changing the bias morphs the output into another logic operation, AND(NAND), whose probability displays analogous behavior. Furthermore, we highlight the possibility of processing two logic gates in parallel in our laser system by exploiting two coupled orthogonal polarizations that can be detected simultaneously. This suggests that the computational power of the optical system may be enhanced by this additional potential for parallel processing.
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http://dx.doi.org/10.1103/PhysRevE.83.046219DOI Listing
April 2011

Stochastic resonance in coupled underdamped bistable systems.

Phys Rev E Stat Nonlin Soft Matter Phys 2010 Oct 28;82(4 Pt 2):046224. Epub 2010 Oct 28.

Physikalische und Theoretische Chemie, Freie University in Berlin, Takustr 3, 14195 Berlin, Germany.

We study onset and control of stochastic resonance (SR) phenomenon in two driven bistable systems, mutually coupled and subjected to independent noises, taking into account the influence of both the inertia and the coupling. In the absence of coupling, we found two critical damping parameters: one for the onset of SR and another for which SR is optimum. We then show that in weakly coupled systems, emergence of SR is governed by chaos. A strong coupling between the two oscillators induces coherence in the system; however, the systems do not synchronize no matter what the coupling is. Moreover, a specific coupling parameter is found for which the SR of each subsystem is optimum. Finally, a scheme for controlling SR in such coupled systems is proposed by introducing a phase difference between the two coherent driving forces.
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http://dx.doi.org/10.1103/PhysRevE.82.046224DOI Listing
October 2010

Optimal stochastic enhancement of photoionization.

Phys Rev Lett 2007 Apr 20;98(16):160201. Epub 2007 Apr 20.

Max Planck Institute for the Physics of Complex Systems, Nöthnitzer Strasse 38, D-01187 Dresden, Germany.

The effect of noise on the nonlinear photoionization of an atom due to a femtosecond pulse is investigated in the framework of the stochastic Schrödinger equation. A modest amount of white noise results in an enhancement of the net ionization yield by several orders of magnitude, giving rise to a form of quantum stochastic resonance. We demonstrate that this effect is preserved if the white noise is replaced by broadband chaotic light.
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http://dx.doi.org/10.1103/PhysRevLett.98.160201DOI Listing
April 2007
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