21,878 research outputs found
Temperature reducing coating for metals subject to flame exposure Patent
Anodizing method for providing metal surfaces with temperature reducing coatings against flame
Direct images of bundles under Frobenius morphisms
Let be a smooth projective variety of dimension over an algebraically
closed field with and be the relative
Frobenius morphism. For any vector bundle on , we prove that instability
of is bounded by instability of
()(Corollary \ref{cor3.8}). When is a smooth
projective curve of genus , it implies being stable whenever
is stable.Comment: the final version to appear in Invent. math. (2008
A-infinity algebra of an elliptic curve and Eisenstein series
We compute explicitly the A-infinity structure on the Ext-algebra of the
collection , where is a line bundle of degree 1 on an
elliptic curve . The answer involves higher derivatives of Eisenstein
series.Comment: 13 pages, 3 figures; v3: added remark on the limit at the cus
Collisional decay of a strongly driven Bose-Einstein condensate
We study the collisional decay of a strongly driven Bose-Einstein condensate
oscillating between two momentum modes. The resulting products of the decay are
found to strongly deviate from the usual s-wave halo. Using a stochastically
seeded classical field method we simulate the collisional manifold. These
results are also explained by a model of colliding Bloch states.Comment: 4 pages, 4 figure
Accurate determination of the Lagrangian bias for the dark matter halos
We use a new method, the cross power spectrum between the linear density
field and the halo number density field, to measure the Lagrangian bias for
dark matter halos. The method has several important advantages over the
conventional correlation function analysis. By applying this method to a set of
high-resolution simulations of 256^3 particles, we have accurately determined
the Lagrangian bias, over 4 magnitudes in halo mass, for four scale-free models
with the index n=-0.5, -1.0, -1.5 and -2.0 and three typical CDM models. Our
result for massive halos with ( is a characteristic non-linear
mass) is in very good agreement with the analytical formula of Mo & White for
the Lagrangian bias, but the analytical formula significantly underestimates
the Lagrangian clustering for the less massive halos $M < M_*. Our simulation
result however can be satisfactorily described, with an accuracy better than
15%, by the fitting formula of Jing for Eulerian bias under the assumption that
the Lagrangian clustering and the Eulerian clustering are related with a linear
mapping. It implies that it is the failure of the Press-Schechter theories for
describing the formation of small halos that leads to the inaccuracy of the Mo
& White formula for the Eulerian bias. The non-linear mapping between the
Lagrangian clustering and the Eulerian clustering, which was speculated as
another possible cause for the inaccuracy of the Mo & White formula, must at
most have a second-order effect. Our result indicates that the halo formation
model adopted by the Press-Schechter theories must be improved.Comment: Minor changes; accepted for publication in ApJ (Letters) ; 11 pages
with 2 figures include
Gallium Arsenide Monolithic Optoelectronic Circuits
The optical properties of GaAs make it a very useful material for the fabrication of optical emitters and detectors. GaAs also possesses electronic properties which allow the fabrication of high speed electronic devices which are superior to conventional silicon devices. Monolithic optoelectronic circuits are formed by the integration of optical and electronic devices on a single GaAs substrate. Integration of many devices is most easily accomplished on a semi-insulating (SI) sub-strate. Several laser structures have been fabricated on SI GaAs substrates. Some of these lasers have been integrated with Gunn diodes and with metal semiconductor field effect transistors (MESFETs). An integrated optical repeater has been demonstrated in which MESFETs are used for optical detection and electronic amplification, and a laser is used to regenerate the optical signal. Monolithic optoelectronic circuits have also been constructed on conducting substrates. A heterojunction bipolar transistor driver has been integrated with a laser on an n-type GaAs substrate
Monolithic integration of a GaAlAs buried-heterostructure laser and a bipolar phototransistor
A GaAlAs buried-heterostructure laser has been monolithically integrated with a bipolar phototransistor. The heterojunction transistor was formed by the regrowth of the burying layers of the laser. Typical threshold current values for the lasers were 30 mA. Common-emitter current gains for the phototransistor of 100–400 and light responsivity of 75 A/W (for wavelengths of 0.82 µm) at collector current levels of 15 mA were obtained
Some Sociological Observations on the Response of Israeli Organizations to New Immigrants
Preliminary observation suggests that the contact between Israeli officials and newly arrived immigrants from traditional societies is considerably less bureaucratic than might have been predicted. For example, analysis of several cases of such bureaucrat-client relationships indicates that officials often add the role of teacher to their relatively specific roles as bureaucrats by teaching newcomers how to perform in the role. Moreover, the official often becomes not only a teacher but also a kind of informal leader. This indicates that under certain conditions, formal organizations may give birth to incipient social movements, a direction of organizational change wholly unanticipated in the theoretical literature. The case material is analyzed in terms of (1) a theory of role impingement in which bureaucratic roles are seen to become intertwined with roles that are bureaucratically irrelevant to the conduct of formal organization and (2) a theory of socialization where the official serves as socializing agent for his clients
Quantum Wall Crossing in N=2 Gauge Theories
We study refined and motivic wall-crossing formulas in N=2 supersymmetric
gauge theories with SU(2) gauge group and N_f < 4 matter hypermultiplets in the
fundamental representation. Such gauge theories provide an excellent testing
ground for the conjecture that "refined = motivic."Comment: 24 pages, 4 figure
Optically-Induced Polarons in Bose-Einstein Condensates: Monitoring Composite Quasiparticle Decay
Nonresonant light-scattering off atomic Bose-Einstein condensates (BECs) is
predicted to give rise to hitherto unexplored composite quasiparticles:
unstable polarons, i.e., local ``impurities'' dressed by virtual phonons.
Optical monitoring of their spontaneous decay can display either Zeno or
anti-Zeno deviations from the Golden Rule, and thereby probe the temporal
correlations of elementary excitations in BECs.Comment: 4 pages, 3 figure
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