2,249 research outputs found
Cryogenic Magneto-Terahertz Scanning Near-field Optical Microscope (cm-SNOM)
We have developed a versatile near-field microscopy platform that can operate
at high magnetic fields and below liquid-helium temperatures. We use this
platform to demonstrate an extreme terahertz (THz) nanoscope operation and to
obtain the first cryogenic magneto-THz time-domain nano-spectroscopy/imaging at
temperatures as low as 1.8 K and magnetic fields of up to 5 T simultaneously.
Our cryogenic magneto-THz scanning near-field optical microscopy, or cm-SNOM,
instrument comprises three main equipment: i) a 5 T split pair magnetic
cryostat with a custom made insert for mounting SNOM inside; ii) an atomic
force microscope (AFM) unit that accepts ultrafast THz excitation and iii) a
MHz repetition rate, femtosecond laser amplifier for high-field THz pulse
generation and sensitive detection. We apply the cm-SNOM to obtain proof of
principle measurements of superconducting and topological materials. The new
capabilities demonstrated break grounds for studying quantum materials that
requires extreme environment of cryogenic operation and applied magnetic fields
simultaneously in nanometer space, femtosecond time, and terahertz energy
scales
Van der Waals epitaxy of Bi2Se3 on Si(111) vicinal surface: An approach to prepare high-quality thin films of topological insulator
Epitaxial growth of topological insulator Bi2Se3 thin films on nominally flat
and vicinal Si(111) substrates is studied. In order to achieve planner growth
front and better quality epifilms, a two-step growth method is adopted for the
van der Waal epitaxy of Bi2Se3 to proceed. By employing vicinal Si(111)
substrate surfaces, the in-pane growth rate anisotropy of Bi2Se3 is explored to
achieve single crystalline Bi2Se3 epifilms, in which threading defects and
twins are effectively suppressed. Optimization of the growth parameters has
resulted in vicinal Bi2Se3 films showing a carrier mobility of ~ 2000 cm2V-1s-1
and the background doping of ~ 3 x 1018 cm-3 of the as-grown layers. Such
samples not only show relatively high magnetoresistance but also a linear
dependence on magnetic field.Comment: 18 pages, 4 figure
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Linoleic acid participates in the response to ischemic brain injury through oxidized metabolites that regulate neurotransmission.
Linoleic acid (LA; 18:2 n-6), the most abundant polyunsaturated fatty acid in the US diet, is a precursor to oxidized metabolites that have unknown roles in the brain. Here, we show that oxidized LA-derived metabolites accumulate in several rat brain regions during CO2-induced ischemia and that LA-derived 13-hydroxyoctadecadienoic acid, but not LA, increase somatic paired-pulse facilitation in rat hippocampus by 80%, suggesting bioactivity. This study provides new evidence that LA participates in the response to ischemia-induced brain injury through oxidized metabolites that regulate neurotransmission. Targeting this pathway may be therapeutically relevant for ischemia-related conditions such as stroke
Exact calculation of the skyrmion lifetime in a ferromagnetic Bose condensate
The tunneling rate of a skyrmion in ferromagnetic spin-1/2 Bose condensates
through an off-centered potential barrier is calculated exactly with the
periodic instanton method. The prefactor is shown to depend on the chemical
potential of the core atoms, at which level the atom tunnels. Our results can
be readily extended to estimate the lifetime of other topological excitations
in the condensate, such as vortices and monopoles.Comment: 16 pages, 4 figures, to appear Phys. Rev.
Detecting massive gravitons using pulsar timing arrays
Massive gravitons are features of some alternatives to general relativity.
This has motivated experiments and observations that, so far, have been
consistent with the zero mass graviton of general relativity, but further tests
will be valuable. A basis for new tests may be the high sensitivity
gravitational wave experiments that are now being performed, and the higher
sensitivity experiments that are being planned. In these experiments it should
be feasible to detect low levels of dispersion due to nonzero graviton mass.
One of the most promising techniques for such a detection may be the pulsar
timing program that is sensitive to nano-Hertz gravitational waves.
Here we present some details of such a detection scheme. The pulsar timing
response to a gravitational wave background with the massive graviton is
calculated, and the algorithm to detect the massive graviton is presented. We
conclude that, with 90% probability, massles gravitons can be distinguished
from gravitons heavier than eV (Compton wave length
km), if biweekly observation of 60 pulsars
are performed for 5 years with pulsar RMS timing accuracy of 100 ns. If 60
pulsars are observed for 10 years with the same accuracy, the detectable
graviton mass is reduced to eV ( km); for 5-year observations of 100 or 300 pulsars, the sensitivity is
respectively ( km) and
eV ( km). Finally, a 10-year
observation of 300 pulsars with 100 ns timing accuracy would probe graviton
masses down to eV ( km).Comment: 13 pages, 5 figures, Accepted by Ap
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Cathelicidin preserves intestinal barrier function in polymicrobial sepsis.
ObjectivesThe intestinal epithelium compartmentalizes the sterile bloodstream and the commensal bacteria in the gut. Accumulating evidence suggests that this barrier is impaired in sepsis, aggravating systemic inflammation. Previous studies reported that cathelicidin is differentially expressed in various tissues in sepsis. However, its role in sepsis-induced intestinal barrier dysfunction has not been investigated.DesignTo examine the role of cathelicidin in polymicrobial sepsis, cathelicidin wild-(Cnlp+/+) and knockout (Cnlp-/-) mice underwent cecal-ligation and puncture (CLP) followed by the assessment of septic mortality and morbidity as well as histological, biochemical, immunological, and transcriptomic analyses in the ileal tissues. We also evaluated the prophylactic and therapeutic efficacies of vitamin D3 (an inducer of endogenous cathelicidin) in the CLP-induced murine polymicrobial sepsis model.ResultsThe ileal expression of cathelicidin was increased by three-fold after CLP, peaking at 4βh. Knockout of Cnlp significantly increased 7-day mortality and was associated with a higher murine sepsis score. Alcian-blue staining revealed a reduced number of mucin-positive goblet cells, accompanied by reduced mucin expression. Increased number of apoptotic cells and cleavage of caspase-3 were observed. Cnlp deletion increased intestinal permeability to 4kD fluorescein-labeled dextran and reduced the expression of tight junction proteins claudin-1 and occludin. Notably, circulating bacterial DNA load increased more than two-fold. Transcriptome analysis revealed upregulation of cytokine/inflammatory pathway. Depletion of Cnlp induced more M1 macrophages and neutrophils compared with the wild-type mice after CLP. Mice pre-treated with cholecalciferol (an inactive form of vitamin D3) or treated with 1alpha, 25-dihydroxyvitamin D3 (an active form of VD3) had decreased 7-day mortality and significantly less severe symptoms. Intriguingly, the administration of cholecalciferol after CLP led to worsened 7-day mortality and the associated symptoms.ConclusionsEndogenous cathelicidin promotes intestinal barrier integrity accompanied by modulating the infiltration of neutrophils and macrophages in polymicrobial sepsis. Our data suggested that 1alpha, 25-dihydroxyvitamin D3 but not cholecalciferol is a potential therapeutic agent for treating sepsis
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LNK suppresses interferon signaling in melanoma.
LNK (SH2B3) is a key negative regulator of JAK-STAT signaling which has been extensively studied in malignant hematopoietic diseases. We found that LNK is significantly elevated in cutaneous melanoma; this elevation is correlated with hyperactive signaling of the RAS-RAF-MEK pathway. Elevated LNK enhances cell growth and survival in adverse conditions. Forced expression of LNK inhibits signaling by interferon-STAT1 and suppresses interferon (IFN) induced cell cycle arrest and cell apoptosis. In contrast, silencing LNK expression by either shRNA or CRISPR-Cas9 potentiates the killing effect of IFN. The IFN-LNK signaling is tightly regulated by a negative feedback mechanism; melanoma cells exposed to IFN upregulate expression of LNK to prevent overactivation of this signaling pathway. Our study reveals an unappreciated function of LNK in melanoma and highlights the critical role of the IFN-STAT1-LNK signaling axis in this potentially devastating disease. LNK may be further explored as a potential therapeutic target for melanoma immunotherapy
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Stops making sense: translational trade-offs and stop codon reassignment
Background
Efficient gene expression involves a trade-off between (i) premature termination of protein synthesis; and (ii) readthrough, where the ribosome fails to dissociate at the terminal stop. Sense codons that are similar in sequence to stop codons are more susceptible to nonsense mutation, and are also likely to be more susceptible to transcriptional or translational errors causing premature termination. We therefore expect this trade-off to be influenced by the number of stop codons in the genetic code. Although genetic codes are highly constrained, stop codon number appears to be their most volatile feature.
Results
In the human genome, codons readily mutable to stops are underrepresented in coding sequences. We construct a simple mathematical model based on the relative likelihoods of premature termination and readthrough. When readthrough occurs, the resultant protein has a tail of amino acid residues incorrectly added to the C-terminus. Our results depend strongly on the number of stop codons in the genetic code. When the code has more stop codons, premature termination is relatively more likely, particularly for longer genes. When the code has fewer stop codons, the length of the tail added by readthrough will, on average, be longer, and thus more deleterious. Comparative analysis of taxa with a range of stop codon numbers suggests that genomes whose code includes more stop codons have shorter coding sequences.
Conclusions
We suggest that the differing trade-offs presented by alternative genetic codes may result in differences in genome structure. More speculatively, multiple stop codons may mitigate readthrough, counteracting the disadvantage of a higher rate of nonsense mutation. This could help explain the puzzling overrepresentation of stop codons in the canonical genetic code and most variants
Π€ΠΎΡΠΌΠΈΡΠΎΠ²Π°Π½ΠΈΠ΅ ΠΈ ΡΠ°Π·Π²ΠΈΡΠΈΠ΅ ΡΡΠ½ΠΊΠ° ΡΠΊΠΎΠ»ΠΎΠ³ΠΈΡΠ΅ΡΠΊΠΈ ΡΠΈΡΡΡΡ ΠΏΡΠΎΠ΄ΡΠΊΡΠΎΠ² Π² Π ΠΎΡΡΠΈΠΈ
Π Π°Π±ΠΎΡΠ° Π½Π°ΠΏΡΠ°Π²Π»Π΅Π½Π° Π½Π° Π²ΡΡΠ²Π»Π΅Π½ΠΈΠ΅ ΠΎΡΠΎΠ±Π΅Π½Π½ΠΎΡΡΠ΅ΠΉ ΡΠΎΡΠΌΠΈΡΠΎΠ²Π°Π½ΠΈΡ ΠΈ Π½Π°ΠΏΡΠ°Π²Π»Π΅Π½ΠΈΠΉ ΡΠ°Π·Π²ΠΈΡΠΈΡ ΡΠΎΡΡΠΈΠΉΡΠΊΠΎΠ³ΠΎ ΡΡΠ½ΠΊΠ° ΡΠΊΠΎΠ»ΠΎΠ³ΠΈΡΠ΅ΡΠΊΠΈ ΡΠΈΡΡΠΎΠΉ ΠΏΡΠΎΠ΄ΠΎΠ²ΠΎΠ»ΡΡΡΠ²Π΅Π½Π½ΠΎΠΉ ΠΏΡΠΎΠ΄ΡΠΊΡΠΈΠΈ, Π° ΡΠ°ΠΊ ΠΆΠ΅ Π½Π° ΡΠ°Π·ΡΠ°Π±ΠΎΡΠΊΡ ΠΏΡΠΎΠ³ΡΠ°ΠΌΠΌΡ ΠΏΠΎΠ²ΡΡΠ΅Π½ΠΈΡ ΡΡΡΠ΅ΠΊΡΠΈΠ²Π½ΠΎΡΡΠΈ ΠΈ ΡΡΡΠΎΠΉΡΠΈΠ²ΠΎΡΡΠΈ ΡΡΠ½ΠΊΡΠΈΠΎΠ½ΠΈΡΠΎΠ²Π°Π½ΠΈΡ ΠΏΡΠ΅Π΄ΠΏΡΠΈΡΡΠΈΠΉ Π΄Π°Π½Π½ΠΎΠΉ ΡΡΠ΅ΡΡ Π΄Π΅ΡΡΠ΅Π»ΡΠ½ΠΎΡΡΠΈ.The work is aimed at identifying the features of formation and directions development of the Russian market of ecologically pure food products, and As well as the development of a program to increase efficiency and sustainability Functioning of enterprises in this field of activity
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