Rindler Physics on the String Worldsheet.

We construct the tensionless limit of bosonic string theory in terms of a family of worldsheets with increasing acceleration and show that the null string emerges in the limit of infinite acceleration when the Rindler horizon is hit. We discover a novel phenomenon we call null string complementarity, which gives two distinct observer-dependent pictures of the emergence of open string physics from closed strings in the tensionless limit. The closed string vacuum as observed by the inertial worldsheet turns into a D instanton in the tensionless limit, while in the complementary picture from the accelerated worldsheet, one sees the emergence of a D-25 brane. We finally discuss approaching the Rindler horizon through time evolution at constant acceleration and also show how an open string picture arises very naturally.

Thermoelectric materials taking advantage of spin entropy: lessons from chalcogenides and oxides.

The interplay between charges and spins may influence the dynamics of the carriers and determine their thermoelectric properties. In that respect, magneto-thermoelectric power MTEP, i.e. the measurements of the Seebeck coefficient S under the application of an external magnetic field, is a powerful technique to reveal the role of magnetic moments on S. This is illustrated by different transition metal chalcogenides: CuCrTiS4 and CuMnTiS4 magnetic thiospinels, which are compared with magnetic oxides, Curie-Weiss (CW) paramagnetic misfit cobaltites, ruthenates, either ferromagnetic perovskite or Pauli paramagnet quadruple perovskites, and CuGa1-x Mn x Te2 chalcopyrite telluride and Bi1.99Cr0.01Te3 in which diluted magnetism is induced by 3%-Mn and 1%-Cr substitution, respectively. In the case of a ferromagnet (below TC) and CW paramagnetic materials, the increase of magnetization at low T when a magnetic field is applied is accompanied by a decrease of the entropy of the carriers and hence S decreases. This is consistent with the lack of MTEP in the Pauli paramagnetic quadruple perovskites. Also, no significant MTEP is observed in CuGa1-x Mn x Te2 and Bi1.99Cr0.01Te3, for which Kondo-type interaction between magnetic moments and carriers prevails. In contrast, spin glass CuCrTiS4 exhibits negative MTEP like in ferromagnetic ruthenates and paramagnetic misfit cobaltites. This investigation of some chalcogenides and oxides provides key ingredients to select magnetic materials for which S benefits from spin entropy.

Tensionless Path from Closed to Open Strings.

We reconsider the tensionless limit on bosonic closed string theory, where the 3D Bondi-Metzner-Sachs (BMS) algebra appears as symmetries on the world sheet, as opposed to two copies of the Virasoro algebra in the case of the usual tensile theory. This is an ultrarelativistic limit on the world sheet. We consider the induced representations of the BMS algebra in the oscillator basis and show that the limit takes the tensile closed string vacuum to the "induced" vacuum, which is identified as a Neumann boundary state. Hence, rather remarkably, an open string emerges from closed strings in the tensionless limit. We also follow the perturbative states in the tensile theory in the limit and show that there is a Bose-Einstein-like condensation of all perturbative states on this induced vacuum. This ties up nicely with the picture of the formation of a long string from a gas of strings in the Hagedorn temperature, where the effective string tension goes to zero.

Quantum state complexity meets many-body scars.

Scar eigenstates in a many-body system refers to a small subset of non-thermal finite energy density eigenstates embedded into an otherwise thermal spectrum. This novel non-thermal behaviour has been seen in recent experiments simulating a one-dimensional PXP model with a kinetically-constrained local Hilbert space realised by a chain of Rydberg atoms. We probe these small sets of special eigenstates starting from particular initial states by computing the spread complexity associated to time evolution of the PXP hamiltonian. Since the scar subspace in this model is embedded only loosely, the scar states form a weakly broken representation of the Lie algebra. We demonstrate why a careful usage of the forward scattering approximation (FSA), instead of any other method, is required to extract the most appropriate set of Lanczos coefficients in this case as the consequence of this approximate symmetry. Only such a method leads to a well defined notion of a closed Krylov subspace and consequently, that of spread complexity. We show this using three separate initial states, namely|Z2⟩,|Z3⟩and the vacuum state, due to the disparate classes of scar states hosted by these sectors. We also discuss systematic methods of remedying the imperfections in the FSA setup stemming from these approximate symmetries.

Tailoring thermoelectric performance ofn-type Bi2Te3through defect engineering and conduction band convergence.

Bi2Te3, an archetypical tetradymite, is recognised as a thermoelectric (TE) material of potential application around room temperature. However, large energy gap (ΔEc) between the light and heavy conduction bands results in inferior TE performance in pristine bulkn-type Bi2Te3. Herein, we propose enhancement in TE performance of pristinen-type Bi2Te3through purposefully manipulating defect profile and conduction band convergence mechanism. Twon-type Bi2Te3samples, S1 and S2, are prepared by melting method under different synthesis condition. The structural as well as microstructural evidence of the samples are obtained through powder x-ray diffraction and transmission electron microscopic study. Optothermal Raman spectroscopy is utilized for comprehensive study of temperature dependent phonon vibrational modes and total thermal conductivity (κ) of the samples which further validates the experimentally measured thermal conductivity. The Seebeck coefficient value is significantly increased from 235 µVK-1(sample S1) to 310 µVK-1(sample S2). This is further justified by conduction band convergence, where ΔEcis reduced from 0.10 eV to 0.05 eV, respectively. To verify the band convergence, the double band Pisarenko model is employed. Large power factor (PF) of 2190 µWm-1K-2and lowerκvalue leading toZTof 0.56 at 300 K is gained in S2. The obtainedPFandZTvalue are among the highest values reported for pristinen-type bulk Bi2Te3. In addition, appreciable value of TE quality factor and compatibility factor (2.7 V-1) at room temperature are also achieved, indicating the usefulness of the material in TE module.

Microplastics contamination in two species of gobies and their estuarine habitat of Indian Sundarbans.

Sundarbans, a Ramsar site of India is contaminated with heterogeneous microplastic wastes. Boddart's goggle eye mudskipper and Rubicundus eelgoby, were common gobies of Sundarbans estuary which accumulated microplastics during their normal biological activities. We estimated the abundance of microplastics in water, sediment; skin, gills, bucco-opercular cavity and gastrointestinal tract of these two goby fishes. Microplastic load estimated in gobies were 0.84 and 2.62 particles per fish species with a dominance of transparent, fibrous microplastics with 100-300 µm in length. ATR-FTIR and Raman spectroscopy revealed polyethylene as prevalent polymer. Surface degradations and adsorption of contaminants on microplastic surface were investigated by SEM-EDX analysis. Presence of hazardous polymers influenced high polymer hazard index and potential ecological risk index which indicated acute environmental threat to Sundarbans estuary and its resident organisms. Current study will provide a new information base on the abundance of microplastics and its ecological hazard in this biosphere reserve.

Characterization and ecological risk assessment of microplastics accumulated in sea water, sand, sediment, shell water and selected tissues of hermit crab of Sundarban Biosphere Reserve.

Sundarban, a Ramsar site of India, has been encountering an ecological threat due to the presence of microplastic (MP) wastes generated from different anthropogenic sources. Clibanarius longitarsus, an intertidal hermit crab of Sundarban Biosphere Reserve, resides within the abandoned shell of a gastropod mollusc, Telescopium telescopium. We characterized and estimated the MP in the gills and gut of hermit crab, as well as in the water present in its occupied gastropod shell. The average microplastic abundance in sea water, sand and sediment were 0.175 ± 0.145 MP L-1, 42 ± 15.03 MP kg-1 and 67.63 ± 24.13 MP kg-1 respectively. The average microplastic load in hermit crab was 1.94 ± 0.59 MP crab-1, with 33.89 % and 66.11 % in gills and gut respectively. Gastropod shell water exhibited accumulation of 1.69 ± 1.43 MP L-1. Transparent and fibrous microplastics were documented as the dominant polymers of water, sand and sediment. Shell water exhibited the prevalence of green microplastics followed by transparent ones. Microscopic examination revealed microplastics with 100-300 µm size categories were dominant across all abiotic compartments. ATR-FTIR and Raman spectroscopy confirmed polyethylene and polypropylene as the prevalent polymers among the five identified polymers of biotic and abiotic components. The target group index indicated green and black as the preferable microplastics of crab. The ecological risk analysis indicated a considerable level of environmental pollution risk in Sundarban and its inhabiting organisms. This important information base may facilitate in developing a strategy of mitigation to limit the MP induced ecological risk at Sundarban Biosphere Reserve.

Tuning of thermoelectric performance by modulating vibrational properties in Ni-doped Sb2Te3.

Sb2Te3, a binary chalcogenide-based 3D topological insulator, attracts significant attention for its exceptional thermoelectric performance. We report the vibrational properties of magnetically doped Sb2Te3thermoelectric material. Ni doping induces defect/disorder in the system and plays a positive role in engineering the thermoelectric properties through tuning the vibrational phonon modes. Synchrotron powder x-ray diffraction study confirms good crystalline quality and single-phase nature of the synthesized samples. The change in structural parameters, includingBisoand strain, further corroborate with structural disorder. Detailed modification of phonon modes with doping and temperature variation is analysed from temperature-dependent Raman spectroscopic measurement. Compressive lattice strain is observed from the blue shift of Raman peaks owing to Ni incorporation in Sb site. An attempt is made to extract the lattice thermal conductivity from total thermal conductivity estimated through optothermal Raman studies. Hall concentration data support the change in temperature-dependent resistivity and thermopower. Remarkable increase in thermopower is observed after Ni doping. Simulation of the Pisarenko model, indicating the convergence of the valence band, explains the observed enhancement of thermopower in Sb2-xNixTe3. The energy gap between the light and heavy valence band at Γ point is found to be 30 meV (for Sb2Te3), which is reduced to 3 meV (in Sb1.98Ni0.02Te3). A significant increase in thermoelectric power factor is obtained from 715 µWm-1K-2for pristine Sb2Te3to 2415 µWm-1K-2for Ni-doped Sb2Te3sample. Finally, the thermoelectric figure of merit,ZTis found to increase by four times in Sb1.98Ni0.02Te3than that of its pristine counterpart.

Observation of Griffiths-like phase in the quaternary Heusler compound NiFeTiSn.

The quaternary Heusler compound NiFeTiSn can be considered to be derived from the exotic pseudogap-compound Fe2TiSn by the replacement of one Fe atom by Ni. In contrast to Fe2TiSn, which shows a disorder induced ferromagnetic phase, the ground state of NiFeTiSn is antiferromagnetic with the signature of spin canting. Interestingly, NiFeTiSn shows a Griffiths-like phase characterized by isolated ferromagnetic clusters before attaining the antiferromagnetic state. The Griffiths-like phase is possibly associated with the antisite disorder between Fe and Ti sites as evident from our powder x-ray diffraction study. The compound also shows rather unusual temperature dependence of resistivity, which can be accounted by the prevailing structural disorder in the system. NiFeTiSn turned out to be a rare example where Griffiths-like phase is observed in a semiconducting 3dtransition metal based intermetallic compound with antiferromagnetic ground state.

Variation in the Branching Pattern of Third Part of Axillary Artery- A Case Report.

Anatomical variation of the branching pattern of axillary artery is very common. The knowledge of this variation is often useful during different surgical and interventional procedures. Variations include typically of Lateral Thoracic Artery (LTA) and Posterior Circumflex Humeral Artery (PCHA). The present case has been reported to document the variation of LTA and PCHA. The axilla of a 65-year-old embalmed female cadaver was routinely dissected for educational purpose in the Department of Anatomy, AIIMS, New Delhi, India. Cunnighams Manual of Dissection was followed during the whole dissection procedure. We found that the third part of axillary artery gave rise to a common trunk which divided into PCHA and LTA. The PCHA curved backwards around the humeral neck and made anastomosis with the anterior circumflex humeral artery. The LTA supplied serratus anterior and the pectoral muscles and made anastomosis with intercostal arteries. The axillary nerve accompanied PCHA while the thoracodorsal nerve accompanied LTA. The rare anatomical variation of the branching pattern of axillary artery is assumed to be helpful in the surgical procedures and various therapeutic interventions of the upper limb.

Synthesis of HPMC stabilized nickel nanoparticles and investigation of their magnetic and catalytic properties.

Nickel nanoparticles synthesized from NiCl2·6H2O by hydrazine hydrate in mixed solvent of ethanol and water in the presence of hydroxypropylmethylcellulose (HPMC) as protective and stabilizing agents. The morphology and sizes of synthesized Ni nanoparticles were studied by field-emission-scanning-electron microscopy (FESEM). Structural properties of nanoparticles were examined by X-ray diffraction (XRD). The polymer stabilized Ni nanoparticles were characterized by Fourier-transform infrared (FTIR) spectroscopy. The magnetic measurement showed that the resultant Ni nanoparticles were ferromagnetic. Also, the saturation magnetization (MS), remanent magnetization (MR) and coercivity (MR) were observed to increase with decreasing temperature. The results of magnetic characterization showed that the magnetic properties of the HPMC stabilized Ni nanoparticles are quite different from those of the bared Ni nanoparticles. All the observed magnetic properties essentially reflected the very typical nanoparticle type nature. Consequently, the resulting Ni nanoparticles were found to be highly active and recyclable catalyst for Suzuki coupling reactions.

Nernst quantum oscillations in bulk semi-metals.

With a widely available magnetic field of 10 T, one can attain the quantum limit in bismuth and graphite. At zero magnetic field, these two elemental semi-metals host a dilute liquid of carriers of both signs. All quasi-particles are confined to a few Landau tubes, when the quantum limit is attained. Each time a Landau tube is squeezed before definitely leaving the Fermi surface, the Nernst response sharply peaks. For bismuth, additional Nernst peaks, unexpected in the non-interacting picture, are resolved beyond the quantum limit. The amplitudes of these unexpected Nernst peaks become more pronounced for the samples with the longest electron mean free path.

Effect of 50 MeV Li3+ irradiation on structural and electrical properties of Mn-doped ZnO.

The present work aims to study the effect of ion irradiation on structural and electrical properties and their correlation with the defects in the Zn(1 - x)Mn(x)O-type system. Zn(1 - x)Mn(x)O (x = 0.02, 0.04) samples have been synthesized by the solid-state reaction method and have been irradiated with 50 MeV Li(3+) ions. The concomitant changes have been probed by x-ray diffraction (XRD), temperature-dependent electrical resistivity and positron annihilation lifetime (PAL) spectroscopy. The XRD result shows a single-phase wurtzite structure for Zn(0.98)Mn(0.02)O, whereas for the Zn(0.96)Mn(0.04)O sample an impurity phase has been found, apart from the usual peaks of ZnO. Ion irradiation removes this impurity peak. The grain size of the samples is found to be uniform. For Zn(0.98)Mn(0.02)O, the observed sharp decrease in room temperature resistivity (ρ(RT)) with irradiation is consistent with the lowering of the full width at half maximum of the XRD peaks. However, for Zn(0.96)Mn(0.04)O, ρ(RT) decreases for the initial fluence but increases for a further increase in fluence. All the irradiated Zn(0.98)Mn(0.02)O samples show a metal-semiconductor transition in temperature-dependent resistivity measurements at low temperature. But all the irradiated Zn(0.96)Mn(0.04)O samples show a semiconducting nature in the whole range of temperatures. Results of room temperature resistivity, XRD and PAL measurements are consistent with each other.