Origin of modulated phases and magnetic hysteresis in TmB_4

We investigate the low temperature magnetic phases in TmB_4, a metallic quantum magnet on the geometrically frustrated Shastry-Sutherland lattice, using co-ordinated experimental and theoretical studies. Our results provide an explanation for the appearance of the intriguing fractional plateau in TmB_4 and accompanying magnetic hysteresis. Together with observation of the bump in the half-plateau, our results support the picture that the magnetization plateau structure in TmB_4 is strongly influenced by the zero-field modulated phases. We present a phenomenological model to explain the appearance of the modulated phases and a microscopic Hamiltonian that captures the complete magnetic behavior of TmB_4.Comment: 7 pages, 5 figure

Experimental Investigation of Water Spray Cooling for Temperature Reduction in Liquid Piston Compressor

The objective of this study is to analyze the effect of spray cooling in a liquid piston compressor during the compression of air in terms of temperature abatement and compression efficiency. The liquid piston can effectively cover any irregular containers making its surface area to volume ratio better than conventional reciprocating pistons. This plays an important role in increased heat transfer to the outer surface resulting in improved efficiency. As the compression process has the minimum work input during an isothermal compression, the process path needs to shift from the polytropic curve towards the isothermal curve for higher efficiency. Recently, various methodologies have been tested in the liquid piston for increasing heat transfer from the chamber such as optimal compression trajectories, placing porous media inserts into the chamber, and introducing hollow spheres in the chamber. Also, several studies have presented spray cooling as a viable option for heat transfer enhancement in compressors due to its high specific heat and fine atomization. In this study, to shift compression trajectory towards an isothermal curve, spray cooling is investigated for a compression ratio of 2 in a liquid piston compressor. Experiments are performed in the liquid piston setup with water as the medium and a polypropylene chamber. The experimental setup for the spray system consists of a pump, pressure regulator, flowmeter, data acquisition system, and nozzles. For the spray; full cone and hollow cone nozzles were selected as they provide an even distribution of droplets with moderate to fine diameters. Spray angles from 60° to 120° for full cone nozzles, and injection line pressure from 275 kPa to 550 kPa are tested for various stroke times of compression. A temperature drop from 59°C to 35°C was observed when spray cooling was introduced with a full cone nozzle with 60° spray angle and 275 kPa injection pressure for a compression ratio of 2. Similarly, a significant drop in temperature of the air was observed with the use of spray from hollow cone nozzles with different spray angles and injection pressures. Experimental results indicated that full cone nozzles perform better than hollow cone nozzles due to higher flow rates and an even droplet distribution; even though the hollow cone nozzles have a finer atomization compared to the full cone nozzles. Higher injection line pressures resulted in greater temperature drop because of higher mass loading and finer droplet diameters, however higher injection pressures require higher pump work. Variation in spray angle did not show any significant change in temperature drop. Spray cooling was most effective for shorter compression stroke time along with higher flow rates. The polytropic index of compression approximately changed from 1.2 without spray to 1.04 – 1.08 when spray cooling was introduced. This corresponds to a 9 – 13% improvement in compression efficiency. This shows that by incorporating water spray the efficiency of liquid piston compressors can be significantly improved. Further investigations can be explored for optimization of spray characteristics and with multi-nozzle spray setups for improvements in compressor efficiency

Hysteretic magnetoresistance and unconventional anomalous Hall effect in the frustrated magnet TmB_4

We study TmB_4, a frustrated magnet on the Archimedean Shastry-Sutherland lattice, through magnetization and transport experiments. The lack of anisotropy in resistivity shows that TmB_4 is an electronically three-dimensional system. The magnetoresistance (MR) is hysteretic at low-temperature even though a corresponding hysteresis in magnetization is absent. The Hall resistivity shows unconventional anomalous Hall effect (AHE) and is linear above saturation despite a large MR. We propose that complex structures at magnetic domain walls may be responsible for the hysteretic MR and may also lead to the AHE

Giant magnetoelectric effect in pure manganite-manganite heterostructures

Obtaining strong magnetoelectric couplings in bulk materials and heterostructures is an ongoing challenge. We demonstrate that manganite heterostructures of the form ${\rm (Insulator)/(LaMnO_3)_n/(CaMnO_3)_n/(Insulator)}$ show strong multiferroicity in magnetic manganites where ferroelectric polarization is realized by charges leaking from ${\rm LaMnO_3}$ to ${\rm CaMnO_3}$ due to repulsion. Here, an effective nearest-neighbor electron-electron (electron-hole) repulsion (attraction) is generated by cooperative electron-phonon interaction. Double exchange, when a particle virtually hops to its unoccupied neighboring site and back, produces magnetic polarons that polarize antiferromagnetic regions. Thus a striking giant magnetoelectric effect ensues when an external electrical field enhances the electron leakage across the interface.Comment: 13 page

Quadratic to linear magnetoresistance tuning in TmB4

The change of a material's electrical resistance (R) in response to an external magnetic field (B) provides subtle information for the characterization of its electronic properties and has found applications in sensor and storage related technologies. In good metals, Boltzmann's theory predicts a quadratic growth in magnetoresistance (MR) at low B, and saturation at high fields. On the other hand, a number of nonmagnetic materials with weak electronic correlation and low carrier concentration for metallicity, such as inhomogeneous conductors, semimetals, narrow gap semiconductors and topological insulators, two-dimensional electron gas (2DEG) show positive, non-saturating linear magnetoresistance (LMR). However, observation of LMR in single crystals of a good metal is rare. Here we present low-temperature, angle dependent magnetotransport in single crystals of the antiferromagnetic metal, TmB4. We observe large, positive and anisotropic MR(B), which can be tuned from quadratic to linear by changing the direction of the applied field. In view of the fact that isotropic, single crystalline metals with large Fermi surface (FS) are not expected to exhibit LMR, we attribute our observations to the anisotropic FS topology of TmB4. Furthermore, the linear MR is found to be temperature-independent, suggestive of quantum mechanical origin.Comment: 14 pages, 5 figures, Accepted version of PR

Estimating Gene Signals From Noisy Microarray Images

In oligonucleotide microarray experiments, noise is a challenging problem, as biologists now are studying their organisms not in isolation but in the context of a natural environment. In low photomultiplier tube (PMT) voltage images, weak gene signals and their interactions with the background fluorescence noise are most problematic. In addition, nonspecific sequences bind to array spots intermittently causing inaccurate measurements. Conventional techniques cannot precisely separate the foreground and the background signals. In this paper, we propose analytically based estimation technique. We assume a priori spot-shape information using a circular outer periphery with an elliptical center hole. We assume Gaussian statistics for modeling both the foreground and background signals. The mean of the foreground signal quantifies the weak gene signal corresponding to the spot, and the variance gives the measure of the undesired binding that causes fluctuation in the measurement. We propose a foreground-signal and shapeestimation algorithm using the Gibbs sampling method. We compare our developed algorithm with the existing Mann–Whitney (MW)- and expectation maximization (EM)/iterated conditional modes (ICM)-based methods. Our method outperforms the existing methods with considerably smaller mean-square error (MSE) for all signal-to-noise ratios (SNRs) in computer-generated images and gives better qualitative results in low-SNR real-data images. Our method is computationally relatively slow because of its inherent sampling operation and hence only applicable to very noisy-spot images. In a realistic example using our method, we show that the gene-signal fluctuations on the estimated foreground are better observed for the input noisy images with relatively higher undesired bindings

Interspecies data mining to predict novel ING-protein interactions in human

YesFunding provided by the Open Access Authors Fund