Age Problem in Lemaitre-Tolman-Bondi Void Models

As is well known, one can explain the current cosmic acceleration by considering an inhomogeneous and/or anisotropic universe (which violates the cosmological principle), without invoking dark energy or modified gravity. The well-known one of this kind of models is the so-called Lema\^{\i}tre-Tolman-Bondi (LTB) void model, in which the universe is spherically symmetric and radially inhomogeneous, and we are living in a locally underdense void centered nearby our location. In the present work, we test various LTB void models with some old high redshift objects (OHROs). Obviously, the universe cannot be younger than its constituents. We find that an unusually large $r_0$ (characterizing the size of the void) is required to accommodate these OHROs in LTB void models. There is a serious tension between this unusually large $r_0$ and the much smaller $r_0$ inferred from other observations (e.g. SNIa, CMB and so on). However, if we instead consider the lowest limit 1.7\,Gyr for the quasar APM 08279+5255 at redshift $z=3.91$, this tension could be greatly alleviated.Comment: 17 pages, 9 figures, revtex4; v2: discussions added, Phys. Lett. B in press; v3: published versio

SARS-CoV-2 Host Surface Protease Purification and Inhibitor Identification

With the increasing appearance of highly infectious SARS-CoV-2 variants, mass vaccination becomes a priority for governments around the world. Even if vulnerable populations are vaccinated, antivirals are still required to treat those severely affected by the virus. In the past year, clinical trials have been performed on Camostat mesylate, an inhibitor for the host surface serine protease TMPRSS2, as an antiviral to reduce the severity of SARS-CoV-2 infections. As a general inhibitor for serine proteases, long-term use of Camostat mesylate can lead to the suppression of the patients’ adaptive immune system through off-target inhibition of pro-inflammatory cytokines. In this study, we outline the optimization of expressing and purifying active hTMPRSS2 in E. coli (previously thought to be unfeasible), as well as formulating an in silico and in vitro hybrid HTS pipeline to identify small molecule inhibitors that have higher specificity to the active site of TMPRSS2. After experimenting with different fusion expression constructs and Ni-IMAC purification protocols, the autocatalytic conditions to yield active TMPRSS2 were found to require low salt (150 mM NaCl 50 mM Tris pH 8.0) and given at least 72 hours at 4 oC. Following the successful generation of a quality homology model, successful in silico screening results yielded compounds with a maximum of 15-fold higher binding affinity to the active site of TMPRSS2 compared to Camostat. With an in vitro hit rate of 10% after enriching a commercially available compound library (N = 264, 158 compounds), a patented compound (CIVICYXXDIQUPZ-UHFFFAOYSA-N) was found to inhibit TMPRSS2 to the same degree as recognized antiviral Camostat mesylate with higher binding specificity

New Generalizations of Cosmography Inspired by the Pade Approximant

The current accelerated expansion of the universe has been one of the most important fields in physics and astronomy since 1998. Many cosmological models have been proposed in the literature to explain this mysterious phenomenon. Since the nature and cause of the cosmic acceleration are still unknown, model-independent approaches to study the evolution of the universe are welcome. One of the powerful model-independent approaches is the so-called cosmography. It only relies on the cosmological principle, without postulating any underlying theoretical model. However, there are several shortcomings in the usual cosmography. For instance, it is plagued with the problem of divergence (or an unacceptably large error), and it fails to predict the future evolution of the universe. In the present work, we try to overcome or at least alleviate these problems, and we propose two new generalizations of cosmography inspired by the Pad\'e approximant. One is to directly parameterize the luminosity distance based on the Pad\'e approximant, while the other is to generalize cosmography with respect to a so-called $y_\beta$-shift $y_\beta=z/(1+\beta z)$, which is also inspired by the Pad\'e approximant. Then, we confront them with the observational data with the help of the Markov chain Monte Carlo (MCMC) code emcee, and find that they work fairly well.Comment: 16 pages, 3 tables, 5 figures, revtex4; v2: discussions added, Eur. Phys. J. C in press; v3: published versio

Kondo regime of the impurity spectral function and the current noise spectrum in the double impurity Anderson model

The dissipaton equations of motion (DEOM) method is one of the most popular methods for simulating quantum impurity systems. In this article, we use DOEM theory to deal with the Kondo problem of the double quantum dots (DQDs) impurity system. We focus on the impurity spectral function and the total noise spectral function, this two function will be used to describe the Kondo effect of this system. The influence of the interaction, the hooping and the difference of the chemical potential between the two dots on the Kondo effect of the system is studied. We find that the interaction between the two dots can influence the Kondo effect of the system a lot