1,485 research outputs found
Limits of Binaries That Can Be Characterized by Gravitational Microlensing
Due to the high efficiency of planet detections, current microlensing planet
searches focus on high-magnification events. High-magnification events are
sensitive to remote binary companions as well and thus a sample of
wide-separation binaries are expected to be collected as a byproduct. In this
paper, we show that characterizing binaries for a portion of this sample will
be difficult due to the degeneracy of the binary-lensing parameters. This
degeneracy arises because the perturbation induced by the binary companion is
well approximated by the Chang-Refsdal lensing for binaries with separations
greater than a certain limit. For binaries composed of equal mass lenses, we
find that the lens binarity can be noticed up to the separations of
times of the Einstein radius corresponding to the mass of each lens. Among
these binaries, however, we find that the lensing parameters can be determined
only for a portion of binaries with separations less than times of
the Einstein radius.Comment: 5 pages, 3 figures, 1 tabl
Programmable stimulator system for study of cardiac arrhythmias
Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1993.Includes bibliographical references (p. 123-[125]).by Andrew H. Chung.M.S
Properties of Central Caustics in Planetary Microlensing
To maximize the number of planet detections, current microlensing follow-up
observations are focusing on high-magnification events which have a higher
chance of being perturbed by central caustics. In this paper, we investigate
the properties of central caustics and the perturbations induced by them. We
derive analytic expressions of the location, size, and shape of the central
caustic as a function of the star-planet separation, , and the planet/star
mass ratio, , under the planetary perturbative approximation and compare the
results with those based on numerical computations. While it has been known
that the size of the planetary caustic is \propto \sqrt{q}, we find from this
work that the dependence of the size of the central caustic on is linear,
i.e., \propto q, implying that the central caustic shrinks much more rapidly
with the decrease of compared to the planetary caustic. The central-caustic
size depends also on the star-planet separation. If the size of the caustic is
defined as the separation between the two cusps on the star-planet axis
(horizontal width), we find that the dependence of the central-caustic size on
the separation is \propto (s+1/s). While the size of the central caustic
depends both on and q, its shape defined as the vertical/horizontal width
ratio, R_c, is solely dependent on the planetary separation and we derive an
analytic relation between R_c and s. Due to the smaller size of the central
caustic combined with much more rapid decrease of its size with the decrease of
q, the effect of finite source size on the perturbation induced by the central
caustic is much more severe than the effect on the perturbation induced by the
planetary caustic. Abridged.Comment: 5 pages, 4 figures, ApJ accepte
Ubiquitin ligase MKRN1 modulates telomere length homeostasis through a proteolysis of hTERT
Telomere homeostasis is regulated by telomerase and a collection of associatedproteins. Telomerase is, in turn, regulated by post-translational modifications of the rate-limiting catalytic subunit hTERT. Here we show that disruption of Hsp90 by geldanamycin promotes efficient ubiquitination and proteasome-mediated degradation of hTERT. Furthermore, we have used the yeast two-hybrid method to identify a novel RING finger gene (MKRN1) encoding an E3 ligase that mediates ubiquitination of hTERT. Overexpression of MKRN1 in telomerase-positive cells promotes the degradation of hTERT and decreases telomerase activity and subsequently telomere length. Our data suggest that MKRN1 plays an important role in modulating telomere length homeostasis through a dynamic balance involving hTERT protein stability
Pembrolizumab alone or in combination with chemotherapy as first-line therapy for patients with advanced gastric or gastroesophageal junction adenocarcinoma: results from the phase II nonrandomized KEYNOTE-059 study
BACKGROUND:
The multicohort, phase II, nonrandomized KEYNOTE-059 study evaluated pembrolizumabâ±âchemotherapy in advanced gastric/gastroesophageal junction cancer. Results from cohorts 2 and 3, evaluating first-line therapy, are presented.
METHODS:
Patients â„â18 years old had previously untreated recurrent or metastatic gastric/gastroesophageal junction adenocarcinoma. Cohort 3 (monotherapy) had programmed death receptor 1 combined positive score â„â1. Cohort 2 (combination therapy) received pembrolizumab 200 mg on day 1, cisplatin 80 mg/m2 on day 1 (up to 6 cycles), and 5-fluorouracil 800 mg/m2 on days 1-5 of each 3-week cycle (or capecitabine 1000 mg/m2 twice daily in Japan). Primary end points were safety (combination therapy) and objective response rate per Response Evaluation Criteria in Solid Tumors version 1.1 by central review, and safety (monotherapy).
RESULTS:
In the combination therapy and monotherapy cohorts, 25 and 31 patients were enrolled; median follow-up was 13.8 months (range 1.8-24.1) and 17.5 months (range 1.7-20.7), respectively. In the combination therapy cohort, grade 3/4 treatment-related adverse events occurred in 19 patients (76.0%); none were fatal. In the monotherapy cohort, grade 3-5 treatment-related adverse events occurred in seven patients (22.6%); one death was attributed to a treatment-related adverse event (pneumonitis). The objective response rate was 60.0% [95% confidence interval (CI), 38.7-78.9] (combination therapy) and 25.8% (95% CI 11.9-44.6) (monotherapy).
CONCLUSIONS:
Pembrolizumab demonstrated antitumor activity and was well tolerated as monotherapy and in combination with chemotherapy in patients with previously untreated advanced gastric/gastroesophageal junction adenocarcinoma
The First Comprehensive Photometric Study of the Algol-type System CL Aurigae
We present the first extensive photometric results of CL Aur from our BVRI
CCD photometry made on 22 nights from 2003 November through 2005 February.
Fifteen new timings of minimum light were obtained. During the past 104 years,
the orbital period has varied due to a periodic oscillation superposed on a
continuous period increase. The period and semi-amplitude of the oscillation
are about 21.6 yrs and 0.0133 d, respectively. This detail is interpreted as a
light-travel-time effect due to a low-luminosity K-type star gravitationally
bound to the CL Aur close system. Our photometric study indicates that CL Aur
is a relatively short-period Algol-type binary with values of q=0.602 and
i=88.2. Mass transfer from the secondary to the primary eclipsing
component is at least partly responsible for the observed secular period change
with a rate of dP/dt = +1.4 d yr. A cool spot model has
been calculated but we think that an alternative hot-spot model resulting from
a gas stream impact on the hot star is more reasonable despite two difficulties
with the explanation. Absolute dimensions of the eclipsing system are deduced
and its present state is compared with tracks for single star and conservative
close binary evolution. Finally, we examine the possible reconciliation of two
different calculations of the luminosity of the hot spot and a
re-interpretation of the secular term of the period variability.Comment: 26 pages, including 5 figures and 9 tables, accepted for publication
in A
Critical role of next-nearest-neighbor interlayer interaction in magnetic behavior of magnetic/nonmagnetic multilayers
We report magnetoresistance data in magnetic semiconductor multilayers, which
exhibit a clear step-wise behavior as a function of external field. We
attribute this highly non-trivial step-wise behavior to next-nearest-neighbor
interlayer exchange coupling. Our microscopic calculation suggests that this
next-nearest-neighbor coupling can be as large as 24% of the nearest-neighbor
coupling. It is argued that such unusually long-range interaction is made
possible by the quasi-one-dimensional nature of the system and by the long
Fermi wavelength characteristic of magnetic semiconductors
Band gap opening by two-dimensional manifestation of Peierls instability in graphene
Using first-principles calculations of graphene having high-symmetry
distortion or defects, we investigate band gap opening by chiral symmetry
breaking, or intervalley mixing, in graphene and show an intuitive picture of
understanding the gap opening in terms of local bonding and antibonding
hybridizations. We identify that the gap opening by chiral symmetry breaking in
honeycomb lattices is an ideal two-dimensional (2D) extension of the Peierls
metal-insulator transition in 1D linear lattices. We show that the spontaneous
Kekule distortion, a 2D version of the Peierls distortion, takes place in
biaxially strained graphene, leading to structural failure. We also show that
the gap opening in graphene antidots and armchair nanoribbons, which has been
attributed usually to quantum confinement effects, can be understood with the
chiral symmetry breaking
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