Effects of lengthscales and attractions on the collapse of hydrophobic polymers in water

We present results from extensive molecular dynamics simulations of collapse transitions of hydrophobic polymers in explicit water focused on understanding effects of lengthscale of the hydrophobic surface and of attractive interactions on folding. Hydrophobic polymers display parabolic, protein-like, temperature-dependent free energy of unfolding. Folded states of small attractive polymers are marginally stable at 300 K, and can be unfolded by heating or cooling. Increasing the lengthscale or decreasing the polymer-water attractions stabilizes folded states significantly, the former dominated by the hydration contribution. That hydration contribution can be described by the surface tension model, $\Delta G=\gamma (T)\Delta A$, where the surface tension, $\gamma$, is lengthscale dependent and decreases monotonically with temperature. The resulting variation of the hydration entropy with polymer lengthscale is consistent with theoretical predictions of Huang and Chandler (Proc. Natl. Acad. Sci.,97, 8324-8327, 2000) that explain the blurring of entropy convergence observed in protein folding thermodynamics. Analysis of water structure shows that the polymer-water hydrophobic interface is soft and weakly dewetted, and is characterized by enhanced interfacial density fluctuations. Formation of this interface, which induces polymer folding, is strongly opposed by enthalpy and favored by entropy, similar to the vapor-liquid interface.Comment: 24 pages, 5 figure

Effect of Current Collector and Pyrolysis Temperature on the Electrochemical Performance of Photoresist Derived Carbon Films

SU-8, an epoxy based negative photoresist has been demonstrated as a potential precursor to fabricate thin films and three-dimensional micropatterned arrays in glassy carbon. However, the use of silicon wafer as a substrate cum collector limits their use in real battery devices. In accordance with the commercial lithium ion battery architecture and also owing to enhanced conductivity, we have successfully demonstrated the use of stainless steel (SS) wafer as a current collector to prepare binder free SU-8 derived carbon thin films. Standard carbon microelectromechanical systems (C-MEMS) process parameters were tuned to obtain a uniform, crack-free carbon thin film on SS wafer upon pyrolysis. Further, we varied the final pyrolysis temperature to examine its effect on the microstructure and composition as characterized with X-ray diffraction, Small angle X-ray scattering, Raman spectroscopy and CHNS-O elemental analyzer respectively. The microstructural changes in the carbon films at different pyrolysis temperature were then correlated with their electrochemical performance as investigated using galvanostat charge/discharge experiments, impedance spectroscopy and cyclic voltammetry. Selection of an appropriate current collector and optimizing the pyrolysis temperature yielded excellent cyclic stability and coulombic efficiency with 400 mAh g−1 reversible capacity after 100 cycles, nearly double to as reported in the literature

Linear-in-frequency optical conductivity in GdPtBi due to transitions near the triple points

The complex optical conductivity of the half-Heusler compound GdPtBi is measured in a frequency range from 20 to 22 000 cm$^{-1}$ (2.5 meV - 2.73 eV) at temperatures down to 10 K in zero magnetic field. We find the real part of the conductivity, $\sigma_{1}(\omega)$, to be almost perfectly linear in frequency over a broad range from 50 to 800 cm$^{-1}$ ($\sim$ 6 - 100 meV) for $T \leq 50$ K. This linearity strongly suggests the presence of three-dimensional linear electronic bands with band crossings (nodes) near the chemical potential. Band-structure calculations show the presence of triple points, where one doubly degenerate and one nondegenerate band cross each other in close vicinity of the chemical potential. From a comparison of our data with the optical conductivity computed from the band structure, we conclude that the observed nearly linear $\sigma_{1}(\omega)$ originates as a cumulative effect from all the transitions near the triple points.Comment: 5+ pages, 5 figures, band-structure and optical-conductivity calculations adde

Two-channel conduction in YbPtBi

We investigated transport, magnetotransport, and broadband optical properties of the half-Heusler compound YbPtBi. Hall measurements evidence two types of charge carriers: highly mobile electrons with a temperature-dependent concentration and low-mobile holes; their concentration stays almost constant within the investigated temperature range from 2.5 to 300 K. The optical spectra (10 meV - 2.7 eV) can be naturally decomposed into contributions from intra- and interband absorption processes, the former manifesting themselves as two Drude bands with very different scattering rates, corresponding to the charges with different mobilities. These results of the optical measurements allow us to separate the contributions from electrons and holes to the total conductivity and to implement a two-channel-conduction model for description of the magnetotransport data. In this approach, the electron and hole mobilities are found to be around 50000 and 10 cm$^{2}$/Vs at the lowest temperatures (2.5 K), respectively.Comment: 6 page

Photoresist Derived Carbon Films as High Capacity Anodes for Lithium Ion Battery

An epoxy-based negative photoresist (SU-8) was spin-coated on stainless steel (SS) wafers followed by two-step pyrolysis in inert atmosphere to yield dense carbon films to be used as anodes for lithium (Li) ion batteries. The selection of SS wafer substrates was in accordance with commercial Li ion battery architecture. Cyclic voltammograms confirm the passive layer formation by electrolyte decomposition in the initial cycle. Galvanostatic charge/discharge experiments in the range 0.01-3 V performed at a C-rate=0.1 C confirms the reversible intercalation of Li ions and shows higher gravimetric reversible capacity for these photoresist-derived carbon films on SS wafer substrates than graphite (400 mAh/g vs. 372 mAh/g for graphite). This high reversible capacity may be attributed to high disorder in photoresist derived-carbon as characterized by X-ray diffraction and Raman spectroscopy

Large zero-field cooled exchange-bias in bulk Mn2PtGa

We report a large exchange-bias (EB) effect after zero-field cooling the new tetragonal Heusler compound Mn2PtGa from the paramagnetic state. The first-principle calculation and the magnetic measurements reveal that Mn2PtGa orders ferrimagnetically with some ferromagnetic (FM) inclusions. We show that ferrimagnetic (FI) ordering is essential to isothermally induce the exchange anisotropy needed for the zero-field cooled (ZFC) EB during the virgin magnetization process. The complex magnetic behavior at low temperatures is characterized by the coexistence of a field induced irreversible magnetic behavior and a spin-glass-like phase. The field induced irreversibility originates from an unusual first-order FI to antiferromagnetic transition, whereas, the spin-glass like state forms due to the existence of anti-site disorder intrinsic to the material.Comment: 5 pages, 4 figures, supplementary material included in a separate file; accepted for publication in PR

On the search for the chiral anomaly in Weyl semimetals: The negative longitudinal magnetoresistance

Recently, the existence of massless chiral (Weyl) fermions has been postulated in a class of semi-metals with a non-trivial energy dispersion.These materials are now commonly dubbed Weyl semi-metals (WSM).One predicted property of Weyl fermions is the chiral or Adler-Bell-Jackiw anomaly, a chirality imbalance in the presence of parallel magnetic and electric fields. In WSM, it is expected to induce a negative longitudinal magnetoresistance (NMR), the chiral magnetic effect.Here, we present experimental evidence that the observation of the chiral magnetic effect can be hindered by an effect called "current jetting". This effect also leads to a strong apparent NMR, but it is characterized by a highly non-uniform current distribution inside the sample. It appears in materials possessing a large field-induced anisotropy of the resistivity tensor, such as almost compensated high-mobility semimetals due to the orbital effect.In case of a non-homogeneous current injection, the potential distribution is strongly distorted in the sample.As a consequence, an experimentally measured potential difference is not proportional to the intrinsic resistance.Our results on the MR of the WSM candidate materials NbP, NbAs, TaAs, TaP exhibit distinct signatures of an inhomogeneous current distribution, such as a field-induced "zero resistance' and a strong dependence of the `measured resistance" on the position, shape, and type of the voltage and current contacts on the sample. A misalignment between the current and the magnetic-field directions can even induce a "negative resistance". Finite-element simulations of the potential distribution inside the sample, using typical resistance anisotropies, are in good agreement with the experimental findings. Our study demonstrates that great care must be taken before interpreting measurements of a NMR as evidence for the chiral anomaly in putative Weyl semimetals.Comment: 13 pages, 6 figure

CONCEPT OF AGNI AND AMA IN AYURVEDA - A BRIEF REVIEW

In our country since last few decades along with scientific and technological revolution a social revolution has also took place which ultimately has drastically changed dietary habits of society at large. This change in dietary habit has ultimately resulted in manifestation of many problems related to gastrointestinal tract. Ayurveda, an ancient system of Indian medicine documented and practiced since 1500 B.C. deals with inter-individual variability for personalized and predictive medicine. In Ayurveda the concept of Agni is very specific one of its kind among other contemporary sciences. Concept of Agni is vividly discussed in Ayurveda as it is the most significant entity for maintaining health of an individual. In Ayurveda, Agnimandya is said to be the root cause of most of the diseases. Hence it is important to understand the basic nature of Agni so as to take care of it. In the present study we have reviewed the basic concept of Agni its types thoroughly and also discussed efficacy of some well-known approaches to treat Agnimandya on the basis of recent clinical studies

Not All Comments are Equal: Insights into Comment Moderation from a Topic-Aware Model

Moderation of reader comments is a significant problem for online news platforms. Here, we experiment with models for automatic moderation, using a dataset of comments from a popular Croatian newspaper. Our analysis shows that while comments that violate the moderation rules mostly share common linguistic and thematic features, their content varies across the different sections of the newspaper. We therefore make our models topic-aware, incorporating semantic features from a topic model into the classification decision. Our results show that topic information improves the performance of the model, increases its confidence in correct outputs, and helps us understand the model's outputs