Using improved Ge and Si detectors, better neutron shielding, and increased counting time, the Cryogenic Dark Matter Search (CDMS) experiment has obtained stricter limits on the cross section of weakly interacting massive particles (WIMPs) elastically scattering from nuclei. Increased discrimination against electromagnetic backgrounds and reduction of the neutron flux confirm WIMPcandidate events previously detected by CDMS were consistent with neutrons and give limits on spin-independent WIMP interactions which are > 2× lower than previous CDMS results for high WIMP mass, and which exclude new parameter space for WIMPs with mass between 8-20 GeV c −2 .PACS numbers: 26.65.+t, 95.75.Wx, 14.60.St This Letter reports new exclusion limits from the Cryogenic Dark Matter Search (CDMS) experiment on the wide class of nonluminous, nonbaryonic, weakly interacting massive particles (WIMPs) [1, 2] which could constitute most of the matter in the universe [3]. A natural WIMP candidate is provided by supersymmetry in the form of the stable lightest superpartner, usually taken to be a neutralino of typical mass ∼ 100 GeV/c 2 [2, 4]. Since the WIMPs are expected to be in a roughly isothermal halo within which the visible portion of our galaxy resides, the energy given to a Ge or Si detector nucleus scattered elastically by a WIMP would be only a few to tens of keV [5].Because of this low recoil energy and very low event rate (< 1 event per day per kg of detector mass), it is essential to suppress backgrounds drastically. The CDMS detectors discriminate nuclear recoils (such as would be produced by WIMPs) from electron recoils by measuring both ionization and phonon energy, greatly reducing the otherwise dominant electromagnetic background. The ionization is much less for nuclear than for electron recoils, while the phonon signal enables a determination of the recoil energy. The main remaining background is from neutrons, which produce WIMP-like recoils, and hence must be distinguished by other means. Two are employed: 1) while Ge and Si have similar scattering rates per nucleon for neutrons, Ge is 5-7 times more efficient than Si for coherently scattering WIMPs; 2) a single WIMP will not scatter in more than one detector, while a neutron frequently will.While brief reviews of all parts of the experiment are provided below, most details have been published [6], and therefore the emphasis here will be on the differences from previous work. The previously published results are from three 165 g Ge BLIP (Berkeley Large Ionization-and-Phonon-mediated) and one 100 g Si ZIP (Z-sensitive Ionization and Phonon-mediated) detectors. The latter, employed as one measure of background neutrons, was not used simultaneously with the Ge BLIPs, but rather in a separate run. BLIP detectors determine phonon production from the detector's calorimetric temperature change, whereas ZIP detectors [7] collect athermal phonons to provide both phonon production and position information. Position information can be obtained
A numerical simulation has been performed on the blood flow patterns in a multi-branch artery during an embolization procedure. The procedure, performed with drug-eluting particulates is designed to occlude blood vessels which feed a tumor. As particulates are injected into the blood stream, they interfere with the flow patterns which previously had existed uninterrupted. This interference causes a maldistribution of flow down daughter artery branches. The patterns of maldistribution change as the embolizing particle travels down the artery toward the target or as particles begin to accumulate at the target. A consequence of the alterations of flow patterns is that future injections of particulates may be diverted from their intended targets and may, consequently, travel down non-targeted artery branches towards otherwise healthy tissue.
Abstract.A new technique for determining the depth of expendable bathythermographs (XBTs) is developed. This new method uses a forward-stepping calculation which incorporates all of the forces on the XBT devices during their descent. Of particular note are drag forces which are calculated using a new drag coefficient expression. That expression, obtained entirely from computational fluid dynamic modeling, accounts for local variations in the ocean environment. Consequently, the method allows for accurate determination of depths for any local temperature environment. The results, which are entirely based on numerical simulation, are compared with the experiments of LM Sippican T-5 XBT probes. It is found that the calculated depths differ by less than 3 % from depth estimates using the standard fall-rate equation (FRE). Furthermore, the differences decrease with depth. The computational model allows an investigation of the fluid flow patterns along the outer surface of the probe as well as in the interior channel. The simulations take account of complex flow phenomena such as laminar-turbulent transition and flow separation.
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