674 research outputs found
Monte Carlo studies and optimization for the calibration system of the Gerda experiment
No full textThe GERmanium Detector Array, GERDA, searches for neutrinoless double is decay in Ge-76 using bare highpurity germanium detectors submerged in liquid argon. For the calibration of these detectors 7 emitting sources have to be lowered from their parking position on the top of the cryostat over more than 5 m clown to the germanium crystals. With the help of Monte Carlo simulations, the relevant parameters of the calibration system were determined. It was found that three Th-228 sources with an activity of 20 kBq each at two different vertical positions will be necessary to reach sufficient statistics in all detectors in less than 4 h of calibration time. These sources will contribute to the background of the experiment with a total of (1.07 +/- 0.04(stat) (+0.13)(-0.19)(sys)) is 10(-4) ctsAkeV kg yr)) when shielded from below with 6 cm of tantalum in the parking position. (C) 2013 Elsevier B.V. All rights reserved
Neutrino physics with multi-ton scale liquid xenon detectors
No full textWe study the sensitivity of large-scale xenon detectors to low-energy solar neutrinos,
to coherent neutrino-nucleus scattering and to neutrinoless double beta decay. As
a concrete example, we consider the xenon part of the proposed DARWIN (Dark Matter
WIMP Search with Noble Liquids) experiment. We perform detailed Monte Carlo simulations
of the expected backgrounds, considering realistic energy resolutions and thresholds
in the detector. In a low-energy window of 2–30 keV, where the sensitivity to solar pp and
7Be-neutrinos is highest, an integrated pp-neutrino rate of 5900 events can be reached in a fiducial mass of 14 tons of natural xenon, after 5 years of data. The pp-neutrino flux could thus be measured with a statistical uncertainty around 1%, reaching the precision of solar model predictions. These low-energy solar neutrinos will be the limiting background to the dark matter search channel for WIMP-nucleon cross sections below ~2X 10-48 cm2 and WIMP masses around 50 GeV c 2, for an assumed 99.5% rejection of electronic recoils due to elastic neutrino-electron scatters. Nuclear recoils from coherent scattering of solar neutrinos will limit the sensitivity to WIMP masses below ~6 GeV c-2 to cross sections above ~4X10-45cm2. DARWIN could reach a competitive half-life sensitivity of 5.6X1026 y to the neutrinoless double beta decay of 136Xe after 5 years of data, using 6 tons of natural xenon in the central detector region
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No full textGML4:3:1
No full textPresent status of the Cryogenic Dark Matter Search (CDMS II) experiment D. Abrams a,D.S. Akerib b,M.S. Armel-Funkhouser c,L. Baudis a,D.A. Bauer d, P.L. Brink a, *,R. Bunker d,B. Cabrera a,D.O. Caldwell d,J.P. Castle a,C.L. Chang a
Complementarity of dark matter direct detection targets
No full textWe investigate the reconstruction capabilities of the dark matter mass and spin-independent cross section from future ton-scale direct detection experiments using germanium, xenon, or argon as targets. Adopting realistic values for the exposure, energy threshold, and resolution of dark matter experiments which will come online within 5 to 10 years, the degree of complementarity between different targets is quantified. We investigate how the uncertainty in the astrophysical parameters controlling the local dark matter density and velocity distribution affects the reconstruction. For a 50 GeV WIMP, astrophysical uncertainties degrade the accuracy in the mass reconstruction by up to a factor of ∼4 for xenon and germanium, compared to the case when astrophysical quantities are fixed. However, the combination of argon, germanium, and xenon data increases the constraining power by a factor of ∼2 compared to germanium or xenon alone. We show that future direct detection experiments can achieve self-calibration of some astrophysical parameters, and they will be able to constrain the WIMP mass with only very weak external astrophysical constraints.
© 2011 American Physical Societ
Dei & Superiorum Indultu Dissertationem Iuridicam De Eo Quod Differt Executionem, Occasione L. si vindicari XX. C. de poenis Praeside Dn. Paulo Francisco Romano ... In Academia Lipsiensi d. Ianuar. AC. 1674. H. L. Q. C. ventilandam proponit Leonhardus Baudisius Lig. Siles. Autor
No full textDruckvariante mit Widmung auf der Rückseite des Titelbl., nicht identisch mit VD17 1:002369
The DRIFT Project: Searching for WIMPS with a Directional Detector
No full textA low pressure time projection chamber for the detection of WIMPs is discussed. Discrimination against Compton electron background in such a device should be very good, and directional information about the recoil atoms would be obtainable. If a full 3-D reconstruction of the recoil tracks can be achieved, Monte Carlo studies indicate that a WIMP signal could be identified with high confidence from as few as 30 detected WIMP-nucleus scattering events
Additive Manufactured Polymer-based Biomaterials
No full textIntroduction
Additive manufacturing technologies, esp. based on li¬tho¬graphy (L-AMTs), open the pos¬sibility to pro¬vide pa¬tient-spe¬ci¬fic im¬plants with fea¬ture re-so¬lu¬tions down to the sub-micron range.1,2 Vinyl esters (VE, incl. vinyl carbonates) have been established as bio¬com¬patible pre¬cursor for photo¬polymers,3 which are the ba¬sis for L-AMTs. Esp. in combination with thiols (thiol-ene chemistry) VEs attain reactivities to¬wards photopolymerization comparable with those of acry¬lates, the benchmark materials for L-AMTs, how¬ever, VEs have an about two orders of ma-gni¬tu¬des lower toxicity.4 Moreover, VEs have ve-ry favorable degradation products. Low molecular weight polyvinyl alcohol and carbon acids can be excreted easily and residual monomers hydrolyze to ace¬tic aldehyde.5
Owing their characteristic polymer architecture, pho¬to¬polymers have a very low toughness in general. How¬ever, by application of toughness enhancers, high molecular weight co-monomers as well as chain trans¬fer agents, toughness can be increased to values en¬abling the fixation of the implants by screws.6
Experimental Methods
Synthesis of VEs is either accomplished by lipase (CAL-B) ca¬talyzed trans¬esteri¬fication reactions of desired building blocks (e.g., po¬ly¬ca-pro¬lactone te¬le¬che¬lics, PCL)4 with di¬vi¬nyl adi¬pate or by con¬den¬sa¬tion re¬ac¬tion with vi¬nyl chlo¬ro¬for-mate.6
Besides clas¬si¬cal me¬cha¬nical cha¬rac¬te¬ri¬za¬tion of cu¬red spe¬ci¬mens, RT-NIR-photo¬rheology was em¬ployed to in¬ve¬sti¬ga¬te the pho¬to¬po¬ly¬meri¬zation cha¬rac¬teri¬stics of for¬mu¬lations with dif¬ferent mo-no¬mers and ad¬ditives.7
For ad¬di¬tive ma¬nu¬fac¬tu¬ring a di¬gital light pro¬ces-sing (DLP) L-AMT system with upside-down set-up and an InVision® WUXGA 1080p light engine with 460 nm LED was used (Figure 1).8
Results and Discussion
The facile synthesis VEs enables the generation of a tool¬box system (Figure 2) containing a variety of com¬po¬nents for the formulation of materials with different properties.
Figure 2. Vinyl ester (VE) based monomers: divinyl adipate (1), x-armed PCL-VE (2), gycitol based VE (3), ethylene glycol based VE (4), urethane based VE (5).3-6
An appropriate combination of base monomers (VEs and thiols), additives to adjust the toughness and degradation characteristics, and e.g. hydroxyapatite for bone regeneration, enable the manufacturing of patient specific implants by L-AMT
Medical Devices based on Additive Manufactured Biomaterials
No full textAdditive manufacturing technologies, including lithography (L-AMTs), open the possibility to provide patient-specific implants with feature resolutions down to the sub-micron range. [1,2] As biocompatible photopolymer precursors, the basis for L-AMTs, vinyl esters (VE, incl. vinyl carbonates) have been established, having orders of magnitudes lower toxicity compared to the state-of-the-art acrylate-based monomers [3] as well as favorable poly(vinyl alcohol) as degradation product. The low molecular weight poly(vinyl alcohol) can be excreted easily and residual monomers hydrolyze to acetic aldehyde. [4] In order to increase the reactivity of vinyl esters, they are combined with thiols (thiol-ene chemistry), attaining reactivities comparable with those of acrylates. [5]
A severe drawback of photopolymer based materials is their low impact resistance, owing their characteristic (highly crosslinked) polymer architecture. In order to increase the toughness, impact enhancers were developed, high molecular weight co-monomers as well as chain transfer agents, which are able to increase the toughness of these biocompatible materials and enable the fixation of the planned implants by screws. [6
Lithography-based 3D printing of biocompatible polymers
No full textLithography-based additive manufacturing technologies ("3D printing") enable the generation of arbitrary, highly complex 3D structures with very high resolution. This was one of the main aspects, which attracted the interest of modern medicine. The vision is to be able to fill defects in tissues or whole organs with tailor-made, patient-specific, biocompatible polymeric constructs, which promote the regeneration of the tissue or the organ.
Lithography-based additive manufacturing technologies (L-AMTs) base on the curing of liquid formulations in layer-by-layer fashion by light. Crucial components of such formulations are the photo-curable monomer that bears polymerizable groups, and the photoinitiator that initiates the polymerization by the generation of radicals when exposed to light.
For the design of photopolymers as tissue regeneration scaffolds it is important to consider the mechanical properties of the material (which ideally matches with the properties of the tissue), the characteristics of biodegradation (which should be synchronized with the regeneration of new tissue), and - of course - the biocompatibility, i.e. the material has to promote the attachment of cells and all components, incl. degradation products, should have a very low toxicity.
Here, different approaches to 3D print scaffolds will be presented, introducing the L-AMTs stereolithography (laser- and DLP-based, for resolutions in the range of 20 µm) and two-photon-lithography (for resolutions > 1 µm)
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