Stability of small amplitude normal modes of a Bose-Einstein condensate with a singly quantized vortex confined in an optical lattice

We study the dynamics of a BEC with a singly quantized vortex, placed in the combined potential of a 1-D (2-D) optical lattice and an axi-symmetric harmonic trap. A time-dependent variational Lagrangian analysis shows that an optical lattice helps to stabilize the vortex which in absence of the optical lattice is unstable. We find that the normal modes are stable only if the depth of the optical potential is more than a certain critical value. This critical value of the optical potential depends on the interaction parameter.In general higher the interaction parameter,lower the value of the optical potential required to stabilize the vortex. The BEC with the singly quantized vortex is found to be relatively more unstable in a 2-D optical lattice compared to a 1-D optical lattice.Comment: Revised version with 11 pages including 1 figur

Cavity Quantum Optomechanics of Ultracold Atoms in an Optical Lattice: Normal-Mode Splitting

We consider the dynamics of a movable mirror (cantilever) of a cavity coupled through radiation pressure to the light scattered from ultracold atoms in an optical lattice. Scattering from different atomic quantum states creates different quantum states of the scattered light, which can be distinguished by measurements of the displacement spectrum of the cantilever. We show that for large pump intensities the steady state displacement of the cantilever shows bistable behaviour. Due to atomic back-action, the displacement spectrum of the cantilever is modified and depends on the position of the condensate in the Brillouin zone. We further analyze the occurrence of splitting of the normal mode into three modes due to mixing of the mechanical motion with the fluctuations of the cavity field and the fluctuations of the condensate with finite atomic two-body interaction. The present system offers a novel scheme to coherently control ultracold atoms as well as cantilever dynamics.Comment: 6 figure

Dynamics of a movable micro-mirror in a nonlinear optical cavity

We consider the dynamics of a movable mirror (cantilever) of a nonlinear optical cavity. We show that a $\chi^{(3)}$ medium with a strong Kerr nonlinearity placed inside a cavity inhibits the normal mode splitting (NMS) due to the photon blockade mechanism. This study demonstrates that NMS could be used as a tool to observe the photon blockade effect. We also found that the backaction cooling of the movable mirror is reduced in the presence of the Kerr medium.Comment: 2 figure

Damping in 2D and 3D dilute Bose gases

Damping in 2D and 3D dilute gases is investigated using both the hydrodynamical approach and the Hartree-Fock-Bogoliubov (HFB) approximation . We found that the both methods are good for the Beliaev damping at zero temperature and Landau damping at very low temperature, however, at high temperature, the hydrodynamical approach overestimates the Landau damping and the HFB gives a better approximation. This result shows that the comparison of the theoretical calculation using the hydrodynamical approach and the experimental data for high temperature done by Vincent Liu (PRL {\bf21} 4056 (1997)) is not proper. For two-dimensional systems, we show that the Beliaev damping rate is proportional to $k^3$ and the Landau damping rate is proportional to $T^2$ for low temperature and to $T$ for high temperature. We also show that in two dimensions the hydrodynamical approach gives the same result for zero temperature and for low temperature as HFB, but overestimates the Landau damping for high temperature.Comment: 11 pages, 4 figure

Tkachenko modes and quantum melting of Josephson junction type of vortex array in rotating Bose-Einstein condensate

Using path integral formalism, we show that the Abrikosov-Tkachenko vortex lattice may equivalently be understood as an array of Josephson junctions. The Tkachenko modes are found to be basically equivalent to the low energy excitations (Goldstone modes) of an ordered state. The calculated frequencies are in very good agreement with recent experimental data. Calculations of the fluctuations of the relative displacements of the vortices show that vortex melting is a result of quantum fluctuations around the ordered state due to the low energy excitations (Tkachenko modes)and occurs when the ratio of the kinectic energy to the potential energy of the vortex lattice is 0.001.Comment: revised paper 11 pages with 2 figures, all in Pdf forma

Hypervalent Iodine(III) promoted ring-rearrangement strategies in conformationally rigid ring systems

The ring-rearrangement reactions are among the important class of atom economic chemical transformations as it involves direct construction of carbocylic or heterocyclic rings through bond migration reactions. The usefulness of such operation has been realized by many publications [1] and applications in the field of organic synthesis, medicinal chemistry, natural product synthesis and chemical biology [2]. Moreover, the inclusion of environmental benign hypervalent iodine(III) reagents in such processes allows to design a milder pathway to achieve desired ring-rearrangement reactions [3]. Herein, in the present context we have demonstrated a milder pathway for hypervalent iodine(III) mediated ring contraction of conformationally rigid exocyclic-β-enaminones for the synthesis of cyclopentanones with concurrent cyanation [4]. Furthermore, the synthesized cyclopentanones serves as a basic template for the synthesis of new class of ∂-valerolactams by the applications of hypervalent iodine reagents [5].The work was supported by the Russian Science Foundation grant 19-73-10144 and RFBR grant 18-03-00715

Benchmarking the ability of novel compounds to inhibit SARS-CoV-2 main protease using steered molecular dynamics simulations

Background: The SARS-CoV-2 main protease (Mpro) is an attractive target in the COVID-19 drug development process. It catalyzes the polyprotein's translation from viral RNA and specifies a particular cleavage site. Due to the absence of identical cleavage specificity in human cell proteases, targeting Mpro with chemical compounds can obstruct the replication of the virus. Methods: To explore the potential binding mechanisms of 1,2,3-triazole scaffolds in comparison to co-crystallized inhibitors 11a and 11b towards Mpro, we herein utilized molecular dynamics and enhanced sampling simulation studies. Results and conclusion: All the 1,2,3-triazole scaffolds interacted with catalytic residues (Cys145 and His41) and binding pocket residues of Mpro involving Met165, Glu166, Ser144, Gln189, His163, and Met49. Furthermore, the adequate binding free energy and potential mean force of the topmost compound 3h was comparable to the experimental inhibitors 11a and 11b of Mpro. Overall, the current analysis could be beneficial in developing the SARS-CoV-2 Mpro potential inhibitors. © 2022 Elsevier Ltd5058; Department of Biotechnology, Ministry of Science and Technology, India, DBT; Indian Council of Medical Research, ICMR; Council of Scientific and Industrial Research, India, CSIR; Ministry of Education and Science of the Russian Federation, Minobrnauka: 075-15-2020-777We gratefully acknowledge to the Director, CSIR-Institute of Himalayan Bioresource Technology, Palampur for providing the facilities to carry out this work. This research received no specific grant from any funding agency. The work was carried out under the aegis of the Himalayan Centre for High-throughput Computational Biology (HiCHiCoB), a BIC supported by DBT. The CSIR support in the form of projects MLP:0201 and OLP:0043 for bioinformatics studies is highly acknowledged. R. S. expresses gratitude to the Indian Council of Medical Research, New Delhi, India for providing Senior Research Fellowship. G.V.Z. acknowledge the Ministry of Science and Higher Education of the Russian Federation within the framework of the grant agreement as government subsidies from the Federal budget in accordance with paragraph 4 of article 78.1 of the Budget Code of the Russian Federation (Moscow, October 1, 2020, No. 075-15-2020-777). This manuscript represents CSIR-IHBT communication no. 5058.We gratefully acknowledge to the Director, CSIR-Institute of Himalayan Bioresource Technology, Palampur for providing the facilities to carry out this work. This research received no specific grant from any funding agency. The work was carried out under the aegis of the Himalayan Centre for High-throughput Computational Biology (HiCHiCoB), a BIC supported by DBT. The CSIR support in the form of projects MLP:0201 and OLP:0043 for bioinformatics studies is highly acknowledged. R. S. expresses gratitude to the Indian Council of Medical Research, New Delhi, India for providing Senior Research Fellowship. G.V.Z. acknowledge the Ministry of Science and Higher Education of the Russian Federation within the framework of the grant agreement as government subsidies from the Federal budget in accordance with paragraph 4 of article 78.1 of the Budget Code of the Russian Federation (Moscow, October 1, 2020, No. 075-15-2020-777). This manuscript represents CSIR-IHBT communication no. 5058

CD33M inhibits microglial phagocytosis, migration and proliferation, but the Alzheimer’s disease‐protective variant CD33m stimulates phagocytosis and proliferation, and inhibits adhesion

Funder: Biotechnology and Biological Sciences Research Council; Id: http://dx.doi.org/10.13039/501100000268Abstract: CD33 is a Siglec (sialic acid‐binding immunoglobulin‐type lectin) receptor on microglia. Human CD33 can be alternatively spliced into two isoforms: the long isoform (CD33M) and a shorter isoform (CD33m) that lacks the sialic acid‐binding site. CD33m appears to protect against Alzheimer's disease; however, it remains unclear how. To investigate potential mechanisms by which CD33m may confer protection, we expressed the CD33m and CD33M isoforms of human CD33 in mouse BV‐2 and human CHME3 microglial cells and assessed microglia functions. In the BV‐2 cells, CD33M inhibited microglial phagocytosis of beads, synapses, debris and dead cells, while CD33m increased phagocytosis of beads, debris and cells. RNAi knockdown of the endogenous mouse CD33 increased phagocytosis and prevented CD33m's (but not CD33M’s) effect on phagocytosis. CD33M increased cell attachment but inhibited cell proliferation, while CD33m did the opposite. We also found that CD33M inhibited cell migration. In human CHME3 cells, CD33M increased cell attachment, but inhibited phagocytosis, proliferation and migration, whereas CD33m did the opposite. We conclude that CD33M inhibits microglial phagocytosis, inhibits migration and increases adhesion, while CD33m increases phagocytosis, proliferation and inhibits adhesion. Thus, CD33m might protect against Alzheimer's disease by increasing microglial proliferation, movement and phagocytosis of debris and dead cells. imag

HYPERVALENT IODINE(III) PROMOTED RING-REARRANGEMENT AND ARYLATION STRATEGIES

The chemistry of hypervalent iodine(III) reagents have widely been explored in many organic transformations for the construction of C-C as well as C-N bonds especially for their environmentally benign behavior, low toxicity and milder reaction conditions. The synthetic usefulness of such reagents has been experienced in many ring transformations as well as arylation reactions due to their excellent yield of the products and selectivities.This work was supported by the Russian Science Foundation (# 20-73-10205) and the Russian Foundation for Basic Research (grant # 19-53-55002)