760 research outputs found
Reaction Cycles of Halogen Species in the Immune Defense: Implications for Human Health and Diseases and the Pathology and Treatment of COVID-19
There is no vaccine or specific antiviral treatment for COVID-19. One current
focus is drug repurposing research, but those drugs have limited therapeutic
efficacies and known adverse effects. The pathology of COVID-19 is essentially
unknown. It is therefore challenging to discover a successful treatment to be
approved for clinical use. This paper addresses several key biological
processes of reactive oxygen, halogen and nitrogen species (ROS, RHS and RNS)
that play crucial physiological roles in organisms from plants to humans. These
include why superoxide dismutases, the enzymes to catalyze the formation of
H2O2, are required for protecting ROS-induced injury in cell metabolism, why
the amount of ROS/RNS produced by ionizing radiation at clinically relevant
doses is ~1000 fold lower than the endogenous ROS/RNS level routinely produced
in the cell and why a low level of endogenous RHS plays a crucial role in
phagocytosis for immune defense. Herein we propose a plausible amplification
mechanism in immune defense: ozone-depleting-like halogen cyclic reactions
enhancing RHS effects are responsible for all the mentioned physiological
functions, which are activated by H2O2 and deactivated by NO signaling
molecule. Our results show that the reaction cycles can be repeated thousands
of times and amplify the RHS pathogen-killing (defense) effects by 100,000 fold
in phagocytosis, resembling the cyclic ozone-depleting reactions in the
stratosphere. It is unraveled that H2O2 is a required protective signaling
molecule (angel) in the defense system for human health and its dysfunction can
cause many diseases or conditions such as autoimmune disorders, aging and
cancer. We also identify a class of potent drugs for effective treatment of
invading pathogens such as HIV and SARS-CoV-2 (COVID-19), cancer and other
diseases, and provide a molecular mechanism of action of the drugs or
candidates.Comment: 18 pages, 4 figures, 1 tabl
Theory of magnetoelectric photocurrent generated by direct interband transitions in semiconductor quantum well
A linearly polarized light normally incident on a semiconductor quantum well
with spin-orbit coupling may generate pure spin current via direct interband
optical transition. An electric photocurrent can be extracted from the pure
spin current when an in-plane magnetic field is applied, which has been
recently observed in the InGaAs/InAlAs quantum well [Dai et al., Phys. Rev.
Lett. 104, 246601 (2010)]. Here we present a theoretical study of this
magnetoelectric photocurrent effect associated with the interband transition.
By employing the density matrix formalism, we show that the photoexcited
carrier density has an anisotropic distribution in k space, strongly dependent
on the orientation of the electron wavevector and the polarization of the
light. This anisotropy provides an intuitive picture of the observed dependence
of the photocurrent on the magnetic field and the polarization of the light. We
also show that the ratio of the pure spin photocurrent to the magnetoelectric
photocurrent is approximately equal to the ratio of the kinetic energy to the
Zeeman energy, which enables us to estimate the magnitude of the pure spin
photocurrent. The photocurrent density calculated with the help of an
anisotropic Rashba model and the Kohn-Luttinger model can produce all three
terms in the fitting formula for measured current, with comparable order of
magnitude, but discrepancies are still present and further investigation is
needed.Comment: 13 pages, 9 figures, 2 table
Spin-bias driven magnetization reversal and nondestructive detection in a single molecular magnet
The magnetization reversal in a single molecular magnet (SMM) weakly coupled
to an electrode with spin-dependent splitting of chemical potentials (spin
bias) is theoretically investigated by means of the rate equation. A
microscopic mechanism for the reversal is demonstrated by the avalanche
dynamics at the reversal point. The magnetization as a function of the spin
bias shows hysteresis loops tunable by the gate voltage and varying with
temperature. The nondestructive measurement to the orientation of giant spin in
SMM is presented by measuring the fully polarized electric current in the
response to a small spin bias. For Mnac molecule, its small transverse
anisotropy only slightly violates the results above. The situation when there
is an angle between the easy axis of the SMM and the spin quantization
direction of the electrode is also studied.Comment: 17 pages, 12 figure
Determining coupling dynamic stiffness of structural connection by tested FRFs
Identifying coupling dynamic stiffness of structural connection is often needed in substructural dynamic analysis. To overcome the faultiness of conventional approaches existed, five indirect schemes of inverse substructuring analysis by using tested frequency response functions (FRFs) are provided. And the first indirect scheme is verified by three mass-rubber models constructed as two-level substructures with mono-coupling, bi-coupling and tri-coupling connection. Compared to existing direct scheme of inverse substructuring analysis, it shows better performance with acceptable precision of determining the stiffness
Experimental verification on applying indirect inverse substructuring analysis to identify coupling dynamic stiffness of mechanical assembly via planar surface
To broaden the engineering application of inverse substructuring analysis, the mechanical assembly via planar surface is experimentally studied. Specifically, the first and the second schemes of indirect inverse substructuring analysis are applied to identify the coupling dynamic stiffness of the assembly. The experimental model of the assembly is designed, and the surface is then discretized equivalently into point-to-point connections for testing the frequency response functions (FRFs) involved in the schemes. Experimental results show that, applying both of the schemes are feasible for the identification, and the identified stiffnesses approach to be stable as the number of discretized points increases
Coupling dynamic stiffness identification of mechanical assembly with linear connection by the second indirect scheme of inverse substructuring analysis
A non-ideal connection of mechanical assembly with linear assembling interface is firstly considered in the coupling dynamic stiffness identification by applying the second scheme of indirect inverse substructuring analysis. The experimental model of the mechanical assembly is designed, and the interface is then discretized equivalently as ideal point-coupling for testing the frequency response functions (FRFs) involved in the scheme. As the results of the experimental study, applying the scheme is verified to be feasible for the stiffness identification of a mechanical assembly with linear connection, and the identified stiffness approaches to be stable with increase of the number of discretized points
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