Inertial active harmonic particle with memory induced spreading by viscoelastic suspension.

We investigate the self-propulsion of an inertial active particle confined in a two-dimensional harmonic trap. The particle is suspended in a non-Newtonian or viscoelastic suspension with a friction kernel that decays exponentially with a time constant characterizing the memory timescale or transient elasticity of the medium. By solving the associated non-Markovian dynamics, we identify two regimes in parameter space distinguishing the oscillatory and non-oscillatory behavior of the particle motion. By simulating the particle trajectories and exactly calculating the steady-state probability distribution functions and mean square displacement; interestingly, we observe that with an increase in the memory time scale, the effective temperature of the environment increases. As a consequence, the particle becomes energetic and spread away from the center, covering larger space inside the confinement. On the other hand, with an increase in the duration of the activity, the particle becomes trapped by the harmonic confinement.

Inertial active ratchet: Simulation versus theory.

We present the inertial active dynamics of an Ornstein-Uhlenbeck particle in a piecewise sawtooth ratchet potential. Using the Langevin simulation and matrix continued fraction method (MCFM), the particle transport, steady-state diffusion, and coherence in transport are investigated in different parameter regimes of the model. Spatial asymmetry is found to be a key criterion for the possibility of directed transport in the ratchet. The MCFM results for net particle current of overdamped dynamics of the particle agree well with the simulation results. The simulated particle trajectories for the inertial dynamics and the corresponding position and velocity distribution functions reveal that the system passes through an activity-induced transition in the transport from the running phase to the locked phase of the dynamics. This is further corroborated by the mean square displacement (MSD) calculations, where the MSD gets suppressed with increase in the persistent duration of activity or self-propulsion in the medium and finally approaches zero for a very large value of self propulsion time. The nonmonotonic behavior of the particle current and Péclet number with self-propulsion time confirms that the particle transport and its coherence can be enhanced or reduced by fine tuning the persistent duration of activity. Moreover, for intermediate ranges of self-propulsion time as well as mass of the particle, even though the particle current shows a pronounced unusual maximum with mass, there is no enhancement in the Péclet number, instead the Péclet number decreases with mass, confirming the degradation of coherence in transport.

Manganese substitution induced magnetic transformation and magnetoelectricity in SrFe12O19.

In this study, manganese substituted strontium hexaferrite (SrFe12-xMnxO19; x = 0, 3, 5, and 7) prepared by the sol-gel auto-combustion method are studied. We observed that the substituted Mn preferentially goes to the 2a and 12k sites of Fe. Raman modes related to the 12k site suggest the stiffening of the lattice. The transformation of the grain's shape from hexagonal (x = 0 and 3) to rhombohedral (x = 7) was observed, as shown in the micrographs obtained from FESEM. The thermomagnetic curves show the shift of TC to lower temperatures with the increase in the Mn content. From x = 5 onwards, the growth of another magnetic phase (FiM2) of lower coercivity apart from the parent phase (FiM1) of higher coercivity is seen. The FiM2 phase was found to increase with the Mn content in the sample (16.4(3)% for x = 5 but 66.2(5)% for x = 7). Although the magnetization for both FiM1 and FiM2 decreases with the increase in temperature, both magnetic phases behave in contrast to each other for x = 5 and x = 7. The study suggests a transformation of the compound from high magnetic anisotropy (x = 0) to low magnetic anisotropy (x = 7). The x = 5 composition sample displays the highest value of the first-order ME coefficient (0.83(2) mV × cm-1 × Oe-1). The observed value for x = 5 composition is ∼2.5 times higher than that of the parent x = 0 composition sample (0.33(2) mV × cm-1 × Oe-1). The studies thus suggest that the x = 5 composition is one of the viable candidates for magnetoelectric applications.

Structural Dimensionality Dependence of the Band Gap in An+1BnX3n+1 Ruddlesden-Popper Perovskites: A Global Picture.

Dimensionality engineering in An+1BnX3n+1 Ruddlesden-Popper (RP) perovskites has recently emerged as a promising tool for tuning the band gap to improve optoelectronic properties. However, the evolution of the band gap is dependent on the material; distinguishing the effects of different factors is urgently needed to guide the rational design of high-performance materials. Through first-principles calculations, we perform a systematic investigation of RP oxide, chalcogenide, and halide perovskites. The results reveal that in addition to the confinement effect and the change in octahedral rotation motions and/or amplitudes, interfacial rumpling and a change in the A-site cation coordination number also determine the evolution of the band gap. More importantly, we emphasize that the evolution of the band gap in RP perovskites is not dependent on the material family. Instead, the B-site frontier orbital type (s, p, and d) and bandwidth, A-site cation, interfacial rumpling, and structural distortions simultaneously determine the evolution of the band gap. These insights enable a complete and deeper understanding of various experimental observations.

Inertial active Ornstein-Uhlenbeck particle in the presence of a magnetic field.

We consider an inertial active Ornstein-Uhlenbeck particle in an athermal bath. The particle is charged, constrained to move in a two-dimensional harmonic trap, and a magnetic field is applied perpendicular to the plane of motion. The steady-state correlations and the mean-square displacement are studied when the particle is confined as well as when it is set free from the trap. With the help of both numerical simulation and analytical calculations, we observe that inertia plays a crucial role in the dynamics in the presence of a magnetic field. In a highly viscous medium where the inertial effects are negligible, the magnetic field has no influence on the correlated behavior of position as well as velocity. In the time asymptotic limit, the overall displacement of the confined harmonic particle gets enhanced by the presence of a magnetic field and saturates for a stronger magnetic field. On the other hand, when the particle is set free, the overall displacement gets suppressed and approaches zero when the strength of the field is very high. Interestingly, it is seen that in the time asymptotic limit, the confined harmonic particle behaves like a passive particle and becomes independent of the activity, especially in the presence of a very strong magnetic field. Similarly, for a free particle the mean-square displacement in the long time limit becomes independent of activity even for a longer persistence of noise cor- relation in the dynamics.

Accuracy and speed of elongation in a minimal model of DNA replication.

Being a dual purpose enzyme, the DNA polymerase is responsible for elongation of the newly formed DNA strand as well as cleaving the erroneous growth in case of a misincorporation. The efficiency of replication depends on the coordination of the polymerization and exonuclease activity of DNA polymerase. Here, we propose and analyze a minimal kinetic model of DNA replication and determine exact expressions for the velocity of elongation and the accuracy of replication. We first analyze the case without exonuclease activity. In that case, accuracy is determined by a kinetic competition between stepping and unbinding, with discrimination between correct and incorrect nucleotides in both transitions. We then include exonuclease activity and ask how different modes of additional discrimination in the exonuclease pathway can improve the accuracy while limiting the detrimental effect of exonuclease on the speed of replication. In this way, we ask how the kinetic parameters of the model have to be set to coordinate the two activities of the enzyme for high accuracy and high speed. The analysis also shows that the design of a replication system does not universally have to follow the speed-accuracy trade-off rule, although it does in the biologically realized parameter range. The accuracy of the process is mainly controlled by the crucial role of stepping after erroneous incorporation, which has impact on both polymerase and exonuclease activities of DNA polymerase.

Orbital magnetism of an active particle in viscoelastic suspension.

We consider an active (self-propelling) particle in a viscoelastic fluid. The particle is charged and constrained to move in a two-dimensional harmonic trap. Its dynamics is coupled to a constant magnetic field applied perpendicular to its plane of motion via Lorentz force. Due to the finite activity, the generalized fluctuation-dissipation relation (GFDR) breaks down, driving the system away from equilibrium. While breaking GFDR, we have shown that the system can have finite classical orbital magnetism only when the dynamics of the system contains finite inertia. The orbital magnetic moment has been calculated exactly. Remarkably, we find that when the elastic dissipation timescale of the medium is larger (smaller) than the persistence timescale of the self-propelling particle, it is diamagnetic (paramagnetic). Therefore, for a given strength of the magnetic field, the system undergoes a transition from diamagnetic to paramagnetic state (and vice versa) simply by tuning the timescales of underlying physical processes, such as active fluctuations and viscoelastic dissipation. Interestingly, we also find that the magnetic moment, which vanishes at equilibrium, behaves nonmonotonically with respect to increasing persistence of self-propulsion, which drives the system out of equilibrium.

Giant magnetoelectric effect at the graphone/ferroelectric interface.

Multiferroic heterostructures combining ferromagnetic and ferroelectric layers are promising for applications in novel spintronic devices, such as memories with electrical writing and magnetic reading, assuming their magnetoelectric coupling (MEC) is strong enough. For conventional magnetic metal/ferroelectric heterostructures, however, the change of interfacial magnetic moment upon reversal of the electric polarization is often very weak. Here, by using first principles calculations, we demonstrate a new pathway towards a strong MEC at the interface between the semi-hydrogenated graphene (also called graphone) and ferroelectric PbTiO3. By reversing the polarization of PbTiO3, the magnetization of graphone can be electrically switched on and off through the change of carbon-oxygen bonding at the interface. Furthermore, a ferroelectric polarization can be preserved down to ultrathin PbTiO3 layers less than one nanometer due to an enhancement of the polarization at the interface. The predicted strong magnetoelectric effect in the ultimately thin graphone/ferroelectric layers opens a new opportunity for the electric control of magnetism in high-density devices.

Experimental bovine rotavirus-A (RV-A)infection causes intestinal and extra-intestinal pathology in suckling mice.

We describe here the intestinal and extra-intestinal spread of the species A rotavirus (RV-A) and associated lesions thereof in Swiss albino suckling mice pups, inoculated with a bovine-origin RV-A strain. In total, 35 suckling pups were used, wherein 20 pups received cell culture isolated RV-A @ 160 µL (TCID50/ml, 5 × 106.5) per pup [oral 80 µL and intra peritoneal (IP) 80 µL] and served as an infected group, while 15 pups were kept in the control group and inoculated the same volume of phosphate buffered saline (PBS) of neutral pH orally and IP. Four pups from the infected group and 3 from control group were sacrificed at 3, 5, 7, 9 and 12 day post infection (DPI). Of note, infected pups exhibited signs of dullness and restlessness till 5DPI, but none showed diarrhea at any point of time. No appreciable gross lesions were evident in any of the organs, except for mild congestion of the small intestine and yellowish catarrhal smearing over the luminal surface. However, light microscopic lesions in hematoxylin and eosin (H&E) stained sections of jejunum and ileum revealed vacuolation and pyknosis of nuclei of the mature enterocytes, their lysis and detachment, constriction and detachment of villi, mild mononuclear cells (MNCs) infiltration in the lamina propria and mildcell depletion of Peyer's patches and mesenteric lymph nodes (MLN). The extra-intestinal lesions of the cellular degeneration and mild MNCs infiltration were identified in the liver and kidneys from 3 to 7 DPI, but no lesion was seen in the brain. Interstitial thickening with MNCs of lung parenchyma was visible from 3 to 7 DPI. The lesions in the intestine, lymphoid tissues and lungs resolved after 7 DPI. The presence of viral nucleic acid was seen in the intestinal contents from 3 to 5 DPI by using a RV-A specific reverse-transcription polymerase chain reaction (RT-PCR), while in the MLNs and the lungs it could be detected till 5 DPI by both the RT-PCR and direct fluorescent antigen test (dFAT). However, liver, spleen and brain were tested negative for the presence of RV-A by any of these tests. Nonetheless, the persistence of the RV-A was seen in the MLNs even after the absence of virus from the small intestines. Findings here conclusively indicates that heterologous host origin RV-A has an affinity not only to the intestine but also to extra-intestinal tissues like MLNs and lung tissues.

First report on characterization and pathogenicity study of emerging Lactococcus garvieae infection in farmed rainbow trout, Oncorhynchus mykiss (Walbaum), from India.

"Warm water lactococcosis" in farm-reared rainbow trout, Oncorhynchus mykiss (Walbaum) in the northern Himalayan region of India, caused by bacterium Lactococcus garvieae is described in this study. Nine bacterial isolates were recovered from the organs of haemorrhagic septicaemia rainbow trout and were subjected to biochemical and molecular identification. Cell surface characteristics and virulence of the bacterial isolates are also described. All the nine bacterial isolates had homogenous biochemical characteristics and were Gram-positive, short chains forming (two to eight cells long), α-haemolytic, non-motile ovoid cocci. Partial 16S rDNA nucleotide sequence (~1,400 bp) of current isolates shared 99% identities with the 16S rDNA nucleotide sequence of L. garvieae R421, L. garvieae FMA395 and L. garvieae CAU:1730. The identity of the bacterial isolates was further confirmed by PCR amplification of L. garvieae-specific ~1,100 bp fragment. Transmission electron microscopy (TEM) of one representative isolate, L. garvieae RTCLI04, indicates that the isolated strain lacks thick outer capsule and is of KG+ (non-capsulates) phenotype. An intraperitoneal and intramuscular injection (2.6 × 105 CFU ml-1 ) and also immersion in bacterial suspension @ of 2.6 × 105 CFU ml-1 to healthy rainbow trout juveniles (body weight: 27.5 ± 3.7 g) with L. garvieae RTCLI04 caused 80%, 60% and 10% cumulative mortality in challenged fish, respectively, within 15 days post-infection. The haemorrhagic septicaemic disease was reproduced experimentally. Histopathological examination of organs of experimentally infected fish revealed extensive degenerative and inflammatory changes in eye, kidney, gill and liver. PCR amplification of several putative virulence genes such as haemolysins, adhesins, LPxTG-containing surface proteins and adhesins cluster confirms the virulence of our Indian L. garvieae isolates. To the best of our knowledge, we are reporting for the first time that L. garvieae is associated with fatal haemorrhagic septicaemia in farmed rainbow trout in India.

Strain-induced ferroelectricity and lattice coupling in BaSnO3 and SrSnO3.

Perovskite stannates such as BaSnO3 and SrSnO3 exhibit promising photovoltaic properties, and hold promise for application in solar cell devices. However, the lack of ferroelectricity and the wide band gap in these materials limit their potential for photovoltaic applications. Here, by first-principles calculations, we demonstrate the realization of a primary ferroelectric polarization in non-ferroelectric BaSnO3 and SrSnO3 through strain engineering. In addition to the appearance of polarization, the band gaps of the materials are greatly narrowed when the paraelectric to ferroelectric phase transition takes place under compressive strain. Furthermore, an intriguing Q2 mode triggered by lattice coupling with the polar mode is found in the stannates subjected to a sufficient tensile strain and this mode has a significant effect on the band gap, which suggests another pathway to narrow the band gap through the electric field control of the Q2 mode. The fruitful electronic, structural, and energetic properties are discussed in detail to achieve a fundamental understanding of the strain-induced ferroelectricity, tunable band gap, and lattice couplings between the Q2 mode and different polar/rotational distortions in the perovskite stannates.

Cytomegalovirus-Responsive CD8+ T Cells Expand After Solid Organ Transplantation in the Absence of CMV Disease.

Cytomegalovirus (CMV) is a major cause of morbidity and mortality in solid organ transplant recipients. Approximately 60% of adults are CMV seropositive, indicating previous exposure. Following resolution of the primary infection, CMV remains in a latent state. Reactivation is controlled by memory T cells in healthy individuals; transplant recipients have reduced memory T cell function due to chronic immunosuppressive therapies. In this study, CD8+ T cell responses to CMV polypeptides immediate-early-1 and pp65 were analyzed in 16 CMV-seropositive kidney and heart transplant recipients longitudinally pretransplantation and posttransplantation. All patients received standard of care maintenance immunosuppression, antiviral prophylaxis, and CMV viral load monitoring, with approximately half receiving T cell-depleting induction therapy. The frequency of CMV-responsive CD8+ T cells, defined by the production of effector molecules in response to CMV peptides, increased during the course of 1 year posttransplantation. The increase commenced after the completion of antiviral prophylaxis, and these T cells tended to be terminally differentiated effector cells. Based on this small cohort, these data suggest that even in the absence of disease, antigenic exposure may continually shape the CMV-responsive T cell population posttransplantation.

Tuning the band gap and polarization of BaSnO3/SrSnO3 superlattices for photovoltaic applications.

Band gap and polarization are two important quantities for enhancing the performance of photovoltaic materials. Based on first-principles calculations, we demonstrate that direct band gap and hybrid improper ferroelectric polarization coexist in BaSnO3/SrSnO3 superlattices. Furthermore, the band gap and polarization can be simultaneously tuned by mechanical strain and pressure. In the presence of tensile strain or negative pressure, the band gap is substantially lowered and the polarization is enhanced by about five times in comparison with that without mechanical loads. The lowered band gap is necessary for increasing the efficiency of light absorption, whereas the enhanced polarization is desirable for the separation of photo-excited carriers in the materials. The present work suggests that the strained BaSnO3/SrSnO3 superlattices are promising ferroelectric semiconducting materials for photovoltaic applications.

Hybrid improper ferroelectricity in SrZrO3/BaZrO3 superlattice.

Incipient ferroelectrics, which show a unique dielectric property, arouse tremendous interests due to their potential application in microwave dielectric devices. However, ferroelectric transition in incipient ferroelectrics is suppressed entirely by quantum fluctuation. Here, by means of first-principles calculations, we demonstrate that there exists hybrid improper ferroelectricity in a layered artificial superlattice composed of the incipient ferroelectrics of SrZrO3 and BaZrO3. The hybrid improper ferroelectric polarization stems from oxygen octahedral rotation and coexists with the strain-induced ferroelectric distortion. The coexistence of oxygen octahedral rotation and ferroelectric distortion results in an enhanced polarization in the superlattice. It is further found that the total polarization in the superlattice is mainly contributed by the oxygen octahedral rotation for zero or small strain, whereas the contribution from strain-induced ferroelectric distortion gradually becomes predominant as the strain increases. The phonon dispersion, energy surface and atomic displacements are calculated to shed light on the underlying mechanism of the hybrid improper ferroelectricity in the SrZrO3/BaZrO3 superlattice.

Nanoscale magnetism and novel electronic properties of a bilayer bismuth(111) film with vacancies and chemical doping.

Magnetically doped topological insulators (TIs) exhibit several exotic phenomena including the magnetoelectric effect and quantum anomalous Hall effect. However, from an experimental perspective, incorporation of spin moment into 3D TIs is still challenging. Thus, instead of 3D TIs, the 2D form of TIs may open up new opportunities to induce magnetism. Based on first principles calculations, we demonstrate a novel strategy to realize robust magnetism and exotic electronic properties in a 2D TI [bilayer Bi(111) film: abbreviated as Bi(111)]. We examine the magnetic and electronic properties of Bi(111) with defects such as bismuth monovacancies (MVs) and divacancies (DVs), and these defects decorated with 3d transition metals (TMs). It has been observed that the MV in Bi(111) can induce novel half metallicity with a net magnetic moment of 1 µB. The origin of half metallicity and magnetism in MV/Bi(111) is further explained by the passivation of the σ-dangling bonds near the defect site. Furthermore, in spite of the nonmagnetic nature of DVs, the TMs (V, Cr, Mn, and Fe) trapped at the 5/8/5 defect structure of DVs can not only yield a much higher spin moment than those trapped at the MVs but also display intriguing electronic properties such as metallic, semiconducting and spin gapless semiconducting properties. The predicted magnetic and electronic properties of TM/DV/Bi(111) systems are explained through density of states, spin density distribution and Bader charge analysis.

Interplay of coupling between strain and rotation in ferroelectric SrZrO3/SrTiO3 superlattices.

The combination of oxygen octahedral rotation and epitaxial strain provides a unique opportunity to tune the ferroelectric properties of perovskite superlattices. Here, through first-principles calculations, we demonstrate that the oxygen octahedral rotation predominates the ground state and ferroelectric properties of SrZrO3/SrTiO3 superlattices. The predicted ground state combines the ferroelectric distortion and antiferrodistortive modes simultaneously. The structure-strain phase diagrams of the superlattices are calculated with and without octahedral rotations, which elucidate the interplay of coupling between epitaxial strain and octahedral rotation. It is found that the presence of octahedral rotation not only lowers the energy but also changes the sequence of phase transition from c-r-aa to c-r, in which the coupling of rotation and strain induces an out-of-plane polarization that transforms aa-phase into r-phase.

Mechanical control of magnetism in oxygen deficient perovskite SrTiO3.

Mechanical control of magnetism in perovskite oxides is an important and promising approach in spintronics. Based on the first-principles calculations, we demonstrate that a negative pressure leads to a great enhancement of magnetic moment in deficient SrTiO3 with oxygen vacancies, whereas a positive pressure results in the gradual disappearance of magnetism. Spin charge density, Bader charge analysis and electronic density of states successfully elucidate the origin and underlying physics of the enhancement and disappearance of magnetism. It is found that the split electronic states of dz(2), dyz and dzx in the 3d orbitals of Ti atoms remarkably contribute to the occupancy of majority spin states under negative pressure, which induces a large magnetic moment. Under positive pressure, however, the equal occupancy of both majority and minority t2g and eg states leads to the disappearance of magnetization. In addition, both negative and positive pressures can largely lower the vacancy formation enthalpy, suggesting that the oxygen vacancy is preferable with pressure. Our findings may provide a mechanism to achieve the pressure control of magnetization in nonmagnetic perovskite oxides.