130 research outputs found
The Ori-Soen time machine
Ori and Soen have proposed a spacetime which has closed causal curves on the
boundary of a region of normal causality, all within a region where the weak
energy condition (positive energy density) is satisfied. I analyze the causal
structure of this spacetime in some simplified models, show that the Cauchy
horizon is compactly generated, and argue that any attempt to build such a
spacetime with normal matter might lead to singular behavior where the
causality violation would otherwise take place.Comment: 5 pages, RevTeX, 7 figures with epsf, miscellaneous clarifications in
v2, minor updates to correspond to version to appear in PR
High-resolution microbial community reconstruction by integrating short reads from multiple 16S rRNA regions
The emergence of massively parallel sequencing technology has revolutionized microbial profiling, allowing the unprecedented comparison of microbial diversity across time and space in a wide range of host-associated and environmental ecosystems. Although the high-throughput nature of such methods enables the detection of low-frequency bacteria, these advances come at the cost of sequencing read length, limiting the phylogenetic resolution possible by current methods. Here, we present a generic approach for integrating short reads from large genomic regions, thus enabling phylogenetic resolution far exceeding current methods. The approach is based on a mapping to a statistical model that is later solved as a constrained optimization problem. We demonstrate the utility of this method by analyzing human saliva and Drosophila samples, using Illumina single-end sequencing of a 750 bp amplicon of the 16S rRNA gene. Phylogenetic resolution is significantly extended while reducing the number of falsely detected bacteria, as compared with standard single-region Roche 454 Pyrosequencing. Our approach can be seamlessly applied to simultaneous sequencing of multiple genes providing a higher resolution view of the composition and activity of complex microbial communities
Some remarks on a new exotic spacetime for time travel by free fall
This work is essentially a review of a new spacetime model with closed causal
curves, recently presented in another paper (Class. Quantum Grav.
\textbf{35}(16) (2018), 165003). The spacetime at issue is topologically
trivial, free of curvature singularities, and even time and space orientable.
Besides summarizing previous results on causal geodesics, tidal accelerations
and violations of the energy conditions, here redshift/blueshift effects and
the Hawking-Ellis classification of the stress-energy tensor are examined.Comment: 17 pages, 9 figures. Submitted as a contribution to the proceedings
of "DOMOSCHOOL - International Alpine School of Mathematics and Physics,
Domodossola 2018". Possible text overlaps with my previous work
arXiv:1803.08214, of which this is essentially a review. Additional results
concerning redshift/blueshift effects and the classification of the
stress-energy tensor are presented her
Graphene Bilayer Field-Effect Phototransistor for Terahertz and Infrared Detection
A graphene bilayer phototransistor (GBL-PT) is proposed and analyzed. The
GBL-PT under consideration has the structure of a field-effect transistor with
a GBL as the channel and the back and top gates. The positive bias of the back
gate results in the formation of conducting source and drain sections in the
channel, while the negatively biased top gate provides the potential barrier
which is controlled by the charge of the photogenerated holes. The features of
the GBL-PT operation are associated with the variations of both the potential
distribution and the energy gap in different sections of the channel when the
gate voltages and the charge in the barrier section change. Using the developed
GBL-PT device model, the spectral characteristics, dark current, responsivity
and detectivity are calculated as functions of the applied voltages, energy of
incident photons, intensity of electron and hole scattering, and geometrical
parameters. It is shown that the GBL-PT spectral characteristics are voltage
tuned. The GBL-PT performance as photodetector in the terahertz and infrared
photodetectors can markedly exceed the performance of other photodetectors.Comment: 7 Pages, 7 figure
Class I major histocompatibility complexes loaded by a periodate trigger
Class I major histocompatibility complexes (MHCs) present peptide ligands on the cell surface for recognition by appropriate cytotoxic T cells. The unstable nature of unliganded MHC necessitates the production of recombinant class I complexes through in vitro refolding reactions in the presence of an added excess of peptides. This strategy is not amenable to high-throughput production of vast collections of class I complexes. To address this issue, we recently designed photocaged MHC ligands that can be cleaved by a UV light trigger in the MHC bound state under conditions that do not affect the integrity of the MHC structure. The results obtained with photocaged MHC ligands demonstrate that conditional MHC ligands can form a generally applicable concept for the creation of defined peptide−MHCs. However, the use of UV exposure to mediate ligand exchange is unsuited for a number of applications, due to the lack of UV penetration through cell culture systems and due to the transfer of heat upon UV irradiation, which can induce evaporation. To overcome these limitations, here, we provide proof-of-concept for the generation of defined peptide−MHCs by chemical trigger-induced ligand exchange. The crystal structure of the MHC with the novel chemosensitive ligand showcases that the ligand occupies the expected binding site, in a conformation where the hydroxyl groups should be reactive to periodate. We proceed to validate this technology by producing peptide−MHCs that can be used for T cell detection. The methodology that we describe here should allow loading of MHCs with defined peptides in cell culture devices, thereby permitting antigen-specific T cell expansion and purification for cell therapy. In addition, this technology will be useful to develop miniaturized assay systems for performing high-throughput screens for natural and unnatural MHC ligands
Effects of denosumab in Japanese patients with rheumatoid arthritis treated with conventional antirheumatic drugs: 36-month extension of a Phase III study
Objective. To evaluate the safety and efficacy of long-term denosumab 60 mg every 6 months (Q6M) or every 3 months (Q3M) in patients with rheumatoid arthritis (RA). Methods. This 12-month, randomized, double-blind, placebo-controlled, multicenter, phase III trial with an open-label extension period from 12 to 36 months (DESIRABLE) enrolled Japanese patients with RA treated with placebo (P) for 12 months followed by either denosumab Q6M (P/Q6M) or denosumab Q3M (P/Q3M) for 24 months; denosumab Q6M for 36 months (Q6M/Q6M); or denosumab Q3M for 36 months (Q3M/Q3M). Efficacy was assessed by van der Heijde modified total Sharp score (mTSS), bone erosion score (BES), and joint space narrowing (JSN) score. Results. Long-term treatment better maintained mTSS and BES suppression in the P/Q3M and Q3M/ Q3M vs P/Q6M and Q6M/Q6M groups; changes from baseline in total mTSS (standard error) at 36 months were 2.8 (0.4) and 1.7 (0.3) vs 3.0 (0.4) and 2.4 (0.3), respectively, and corresponding changes in BES were 1.3 (0.2) and 0.4 (0.2) vs 1.4 (0.2) and 1.1 (0.2), respectively. No JSN effect was observed. Bone mineral density consistently increased in all groups after denosumab initiation, regardless of concomitant glucocorticoid administration. Serum C-terminal telopeptide of type I collagen decreased rapidly at 1 month postdenosumab administration (in both the initial 12-month [Q3M and Q6M groups] and long-term treatment [P/Q3M and P/Q6M groups] phases). Adverse event incidence leading to study drug discontinuation was similar across treatment groups. Conclusion. Denosumab treatment maintained inhibition of progression of joint destruction up to 36 months. Based on effects on BES progression, higher dosing frequency at an earlier treatment stage may be needed to optimize treatment. Denosumab was generally well tolerated. (ClinicalTrials.gov: NCT01973569).Pathophysiology and treatment of rheumatic disease
Rotating Black Branes in the presence of nonlinear electromagnetic field
In this paper, we consider a class of gravity whose action represents itself
as a sum of the usual Einstein-Hilbert action with cosmological constant and an
gauge field for which the action is given by a power of the Maxwell
invariant. We present a class of the rotating black branes with Ricci flat
horizon and show that the presented solutions may be interpreted as black brane
solutions with two event horizons, extreme black hole and naked singularity
provided the parameters of the solutions are chosen suitably. We investigate
the properties of the solutions and find that for the special values of the
nonlinear parameter, the solutions are not asymptotically anti-deSitter. At
last, we obtain the conserved quantities of the rotating black branes and find
that the nonlinear source effects on the electric field, the behavior of
spacetime, type of singularity and other quantities.Comment: 7 pages, 5 figures, to appear in EPJ
Surface stresses on a thin shell surrounding a traversable wormhole
We match an interior solution of a spherically symmetric traversable wormhole
to a unique exterior vacuum solution, with a generic cosmological constant, at
a junction interface, and the surface stresses on the thin shell are deduced.
In the spirit of minimizing the usage of exotic matter we determine regions in
which the weak and null energy conditions are satisfied on the junction
surface. The characteristics and several physical properties of the surface
stresses are explored, namely, regions where the sign of the tangential surface
pressure is positive and negative (surface tension) are determined. This is
done by expressing the tangential surface pressure as a function of several
parameters, namely, that of the matching radius, the redshift parameter, the
surface energy density and of the generic cosmological constant. An equation
governing the behavior of the radial pressure across the junction surface is
also deduced.Comment: 24 pages, 11 figures, LaTeX2e, IOP style files. Accepted for
publication in Classical and Quantum Gravity. V2: Four references added, now
25 page
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