492 research outputs found
Finite geometries and diffractive orbits in isospectral billiards
Several examples of pairs of isospectral planar domains have been produced in
the two-dimensional Euclidean space by various methods. We show that all these
examples rely on the symmetry between points and blocks in finite projective
spaces; from the properties of these spaces, one can derive a relation between
Green functions as well as a relation between diffractive orbits in isospectral
billiards.Comment: 10 page
Can One Hear the Shape of a Graph?
We show that the spectrum of the Schrodinger operator on a finite, metric
graph determines uniquely the connectivity matrix and the bond lengths,
provided that the lengths are non-commensurate and the connectivity is simple
(no parallel bonds between vertices and no loops connecting a vertex to
itself). That is, one can hear the shape of the graph! We also consider a
related inversion problem: A compact graph can be converted into a scattering
system by attaching to its vertices leads to infinity. We show that the
scattering phase determines uniquely the compact part of the graph, under
similar conditions as above.Comment: 9 pages, 1 figur
Isospectral domains with mixed boundary conditions
We construct a series of examples of planar isospectral domains with mixed
Dirichlet-Neumann boundary conditions. This is a modification of a classical
problem proposed by M. Kac.Comment: 9 figures. Statement of Theorem 5.1 correcte
Quantum graphs with singular two-particle interactions
We construct quantum models of two particles on a compact metric graph with
singular two-particle interactions. The Hamiltonians are self-adjoint
realisations of Laplacians acting on functions defined on pairs of edges in
such a way that the interaction is provided by boundary conditions. In order to
find such Hamiltonians closed and semi-bounded quadratic forms are constructed,
from which the associated self-adjoint operators are extracted. We provide a
general characterisation of such operators and, furthermore, produce certain
classes of examples. We then consider identical particles and project to the
bosonic and fermionic subspaces. Finally, we show that the operators possess
purely discrete spectra and that the eigenvalues are distributed following an
appropriate Weyl asymptotic law
Silicon Heat Pipe Array
Improved methods of heat dissipation are required for modern, high-power density electronic systems. As increased functionality is progressively compacted into decreasing volumes, this need will be exacerbated. High-performance chip power is predicted to increase monotonically and rapidly with time. Systems utilizing these chips are currently reliant upon decades of old cooling technology. Heat pipes offer a solution to this problem. Heat pipes are passive, self-contained, two-phase heat dissipation devices. Heat conducted into the device through a wick structure converts the working fluid into a vapor, which then releases the heat via condensation after being transported away from the heat source. Heat pipes have high thermal conductivities, are inexpensive, and have been utilized in previous space missions. However, the cylindrical geometry of commercial heat pipes is a poor fit to the planar geometries of microelectronic assemblies, the copper that commercial heat pipes are typically constructed of is a poor CTE (coefficient of thermal expansion) match to the semiconductor die utilized in these assemblies, and the functionality and reliability of heat pipes in general is strongly dependent on the orientation of the assembly with respect to the gravity vector. What is needed is a planar, semiconductor-based heat pipe array that can be used for cooling of generic MCM (multichip module) assemblies that can also function in all orientations. Such a structure would not only have applications in the cooling of space electronics, but would have commercial applications as well (e.g. cooling of microprocessors and high-power laser diodes). This technology is an improvement over existing heat pipe designs due to the finer porosity of the wick, which enhances capillary pumping pressure, resulting in greater effective thermal conductivity and performance in any orientation with respect to the gravity vector. In addition, it is constructed of silicon, and thus is better suited for the cooling of semiconductor devices
Class I and Class II methanol masers in high-mass star forming regions
Among the tracers of the earliest phases in the massive star formation
process, methanol masers have gained increasing importance. The
phenomenological distinction between Class I and II methanol masers is based on
their spatial association with objects such as jets, cores, and ultracompact
HII regions, but is also believed to correspond to different pumping
mechanisms: radiation for Class II masers, collisions for Class I masers. In
this work, we have surveyed a large sample of massive star forming regions -
296 objects divided into two groups named 'High' and 'Low' according to their
[25-12] and [60-12] IRAS colours - in Class I and II methanol masers. Previous
studies indicate that the High sources are likely more evolved. Therefore, the
sample can be used to assess the existence of a sequence for the occurrence of
Class I and II methanol masers during the evolution of a massive star forming
region. We observed the 6 GHz (Class II) CH3OH maser with the Effelsberg 100-m
telescope, and the 44 GHz and 95 GHz (Class I) CH3OH masers with the Nobeyama
45-m telescope. We have detected: 55 sources in the Class II line (12 new
detections); 27 sources in the 44 GHz Class I line (17 new detections); 11
sources in the 95 GHz Class I line (all except one are new detections). Our
statistical analysis shows that the ratio between the detection rates of Class
II and Class I methanol masers is basically the same in High and Low sources.
Therefore, both masers are equally associated with each evolutionary phase. In
contrast, all maser species have about 3 times higher detection rates in High
than in Low sources. This might indicate that the phenomena that originate all
masers become progressively more active with time, during the earliest
evolutionary phases of a high-mass star forming region.Comment: 30 pages including Appendices, 11 figures, accepted for publication
in Astronomy & Astrophysic
Diffractive orbits in isospectral billiards
Isospectral domains are non-isometric regions of space for which the spectra
of the Laplace-Beltrami operator coincide. In the two-dimensional Euclidean
space, instances of such domains have been given. It has been proved for these
examples that the length spectrum, that is the set of the lengths of all
periodic trajectories, coincides as well. However there is no one-to-one
correspondence between the diffractive trajectories. It will be shown here how
the diffractive contributions to the Green functions match nevertheless in a
''one-to-three'' correspondence.Comment: 20 pages, 6 figure
An In Vivo Screen Identifies PYGO2 as a Driver for Metastatic Prostate Cancer
Advanced prostate cancer displays conspicuous chromosomal instability and rampant copy number aberrations, yet the identity of functional drivers resident in many amplicons remain elusive. Here, we implemented a functional genomics approach to identify new oncogenes involved in prostate cancer progression. Through integrated analyses of focal amplicons in large prostate cancer genomic and transcriptomic datasets as well as genes upregulated in metastasis, 276 putative oncogenes were enlisted into an in vivo gain-of-function tumorigenesis screen. Among the top positive hits, we conducted an in-depth functional analysis on Pygopus family PHD finger 2 (PYGO2), located in the amplicon at 1q21.3. PYGO2 overexpression enhances primary tumor growth and local invasion to draining lymph nodes. Conversely, PYGO2 depletion inhibits prostate cancer cell invasion in vitro and progression of primary tumor and metastasis in vivo In clinical samples, PYGO2 upregulation associated with higher Gleason score and metastasis to lymph nodes and bone. Silencing PYGO2 expression in patient-derived xenograft models impairs tumor progression. Finally, PYGO2 is necessary to enhance the transcriptional activation in response to ligand-induced Wnt/β-catenin signaling. Together, our results indicate that PYGO2 functions as a driver oncogene in the 1q21.3 amplicon and may serve as a potential prognostic biomarker and therapeutic target for metastatic prostate cancer.Significance: Amplification/overexpression of PYGO2 may serve as a biomarker for prostate cancer progression and metastasis. Cancer Res; 78(14); 3823-33. ©2018 AACR
A ring laser gyroscope without lock-in phenomenon
We theoretically and numerically study the effect of backscattering on
rotating ring lasers by employing the Maxwell-Bloch equations. We show that
frequency shifts due to the Sagnac effect incorporating the effect of
backscattering can be observed without lock-in phenomenon, if the strength of
backscattering originating in the bumps of the refractive index is larger than
a certain value. It is also shown that the experimental results corresponding
to the theoretical ones can actually be obtained by using a semiconductor
fiber-optic ring laser gyroscope.Comment: 9 pages, 6figure
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