952 research outputs found
Black Lenses in Kaluza-Klein Matter
We present the first examples of formally asymptotically flat black hole
solutions with horizons of general lens space topology . These
5-dimensional static/stationary spacetimes are regular on and outside the event
horizon for any choice of relatively prime integers , in particular
conical singularities are absent. They are supported by Kaluza-Klein matter
fields arising from higher dimensional vacuum solutions through reduction on
tori. The technique is sufficiently robust that it leads to the explicit
construction of regular solutions, in any dimension, realising the full range
of possible topologies for the horizon as well as the domain of outer
communication, that are allowable with multi-axisymmetry. Lastly, as a by
product, we obtain new examples of regular gravitational instantons in higher
dimensions.Comment: 6 pages; Phys. Rev. Lett., to appear; A Quanta Magazine article based
on the results of this paper may be found here:
https://www.quantamagazine.org/mathematicians-find-an-infinity-of-possible-black-hole-shapes-20230124
Dynamics of Extreme Black Holes and Massive String States
In a recent paper, Duff and Rahmfeld argued that certain massive
states of the four-dimensional heterotic string correspond to extreme black
hole solutions. We provide further, dynamical, evidence for this identification
by comparing the scattering of these elementary string states with that of the
corresponding extreme black holes, in the limit of low velocities.Comment: 18 pages, harvma
Micromachinable ultrasonic leaky wave air transducers
Cataloged from PDF version of article.Ultrasonic air transducers using leaky waves on thin membranes are analyzed using perturbation and normal mode approaches. The transducers utilize the efficient coupling of ultrasonic energy to air through radiation of these leaky wave modes when their phase velocity is close to the sound speed in air. Theoretical results on optimum transducer dimensions and bandwidth estimation show that a minimum conversion loss of 8.7 dB with a 78% fractional bandwidth is possible. Common micromachining materials are shown to be suitable transducer materials and result in feasible devices. This is demonstrated by fabricating a 580 kHz transducer using a silicon membrane bonded to a ring of PZT-5H. With this configuration the transducer is self line focusing. Results of through transmission experiments on silicon and transmission images on paper are reported.
© 1998 American Institute of Physic
On the Bartnik extension problem for the static vacuum Einstein equations
We develop a framework for understanding the existence of asymptotically flat
solutions to the static vacuum Einstein equations with prescribed boundary data
consisting of the induced metric and mean curvature on a 2-sphere. A partial
existence result is obtained, giving a partial resolution of a conjecture of
Bartnik on such static vacuum extensions. The existence and uniqueness of such
extensions is closely related to Bartnik's definition of quasi-local mass.Comment: 33 pages, 1 figure. Minor revision of v2. Final version, to appear in
Class. Quantum Gravit
GenSensor Suite: A Web-Based Tool for the Analysis of Gene and Protein Interactions, Pathways, and Regulation
The GenSensor Suite consists of four web tools for elucidating relationships among genes and proteins. GenPath results show which biochemical, regulatory, or other gene set categories are over- or under-represented in an input list compared to a background list. All common gene sets are available for searching in GenPath, plus some specialized sets. Users can add custom background lists. GenInteract builds an interaction gene list from a single gene input and then analyzes this in GenPath. GenPubMed uses a PubMed query to identify a list of PubMed IDs, from which a gene list is extracted and queried in GenPath. GenViewer allows the user to query one gene set against another in GenPath. GenPath results are presented with relevant P- and q-values in an uncluttered, fully linked, and integrated table. Users can easily copy this table and paste it directly into a spreadsheet or document
Intraaortic balloon counterpulsation as a temporary support measure in decompensated critical aortic stenosis
Intraaortic balloon counterpulsation was instituted in two adult patients whose condition was rapidly deteriorating because of critical decompensated valvular aortic stenosis. The acute hemodynamic effect of counterpulsation in these patients was compared with the effect of counterpulsation in three control patients with unstable angina and no aortic valve disease. Augmentation of aortic diastolic pressure was similar in both groups; however, in contrast to the patients with unstable angina, the patients with aortic stenosis had no decrease in left ventricular systolic pressure. Counterpulsation resulted in an increase in the transvalvular pressure gradient, which was associated with a slight increase in stroke volume. In both patients with aortic stenosis, the institution of counterpulsation resulted in marked clinical improvement, which facilitated successful valve replacement surgery.The benefit from counterpulsation in critically decompensated aortic stenosis appears to be derived almost entirely from augmentation of the diastolic coronary filling gradient. The improvement that results from counterpulsation suggests that ischemia is the major cause of decompensation
More on Four-Dimensional Extremal Black Holes
We consider an embedding of the extremal four-dimensional
Reissner-Nordstr\"om black hole into type string theory. The equivalent
type configuration, in the D-brane weak-coupling picture, is a bound
state of D1- and D5-branes threaded by fundamental type strings. The
bound state involves also a NSNS solitonic 5-brane, mimicking the role of the
Kaluza-Klein magnetic monopole. The statistical entropy derived by counting the
degeneracy of the BPS-saturated excitations of this bound state agrees
perfectly with the (semiclassical) Bekenstein-Hawking formula.Comment: 19 pages, using Latex, no figure
Total Widths And Slopes From Complex Regge Trajectories
Maximally complex Regge trajectories are introduced for which both Re
and Im grow as ( small and
positive). Our expression reduces to the standard real linear form as the
imaginary part (proportional to ) goes to zero. A scaling formula for
the total widths emerges: constant for large M, in very
good agreement with data for mesons and baryons. The unitarity corrections also
enhance the space-like slopes from their time-like values, thereby resolving an
old problem with the trajectory in charge exchange. Finally, the
unitarily enhanced intercept, , \nolinebreak is in
good accord with the Donnachie-Landshoff total cross section analysis.Comment: 9 pages, 3 Figure
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