843 research outputs found

    Kaolin shear thickening fluid reinforced UHMWPE composites for protective clothing

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    This study reports the designing and reinforcing of impact resistant textile composites using kaolin based shear thickening colloidal dispersions as the filler material. The reinforced fabric is targeted for the chest protection of cricketers. A shear thickening fluid (STF) has been prepared using kaolin and glycerol, at kaolin volume fractions of 34% and 38%. A combination of mixing techniques including mechanical blending and ultra-sonication are used to prepare the colloidal dispersions. Ultra high molecular weight polyethylene (UHMWPE) woven fabric structures are reinforced with the STF. The fabric coated with STF are then measured for their flexibility, and impact resistance using Shirley stiffness tester and a series of modified drop tower tests respectively. Kaolin STF at 38% volume fraction shows best results in impregnated fabric samples. STF reinforced fabrics provide better impact resistance with improved moisture absorption and flexibility in comparison to the conventional chest guard material

    Gaugino Condensation in M-theory on S^1/Z_2

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    In the low energy limit of for M-theory on S^1/Z_2, we calculate the gaugino condensate potential in four dimensions using the background solutions due to Horava. We show that this potential is free of delta-function singularities and has the same form as the potential in the weakly coupled heterotic string. A general flux quantization rule for the three-form field of M-theory on S^1/Z_2 is given and checked in certain limiting cases. This rule is used to fix the free parameter in the potential originating from a zero mode of the form field. Finally, we calculate soft supersymmetry breaking terms. We find that corrections to the Kahler potential and the gauge kinetic function, which can be large in the strongly coupled region, contribute significantly to certain soft terms. In particular, for supersymmetry breaking in the T-modulus direction, the small values of gaugino masses and trilinear couplings that occur in the weakly coupled, large radius regime are enhanced to order m_3/2 in M-theory. The scalar soft masses remain small even, in the strong coupling M-theory limit.Comment: 20 pages, LATE

    RR-Parity Violation in Flavor Changing Neutral Current Processes and Top Quark Decays

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    We show that supersymmetric RR-parity breaking (̸Rp\not R_p) interactions always result in Flavor Changing Neutral Current (FCNC) processes. Within a single coupling scheme, these processes can be avoided in either the charge +2/3+2/3 or the charge 1/3-1/3 quark sector, but not both. These processes are used to place constraints on \Rp couplings. The constraints on the first and the second generations are better than those existing in the literature. The \Rp interactions may result in new top quark decays. Some of these violate electron-muon universality or produce a surplus of bb quark events in ttˉt\bar{t} decays. Results from the CDF experiment are used to bound these \Rp couplings.Comment: LaTeX, 20 pages, spelling corrected from origina

    A Guide to the threatened and endangered vascular plants of the Lake Mead National Recreation Area

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    This illustrated guide was prepared to provide the botanical community, land managers, and other interested persons with a reference that describes and locates the twelve plant taxa currently being considered by the Fish and Wildlife Service for threatened or endangered status in or around the Lake Mead National Recreation Area. The guide is intended to assist managers of government agencies in determining the presence of these species and in defining management programs for their protection. The guide should be consulted prior to any construction project. If a potential conflict is identified, an onsite evaluation should be conducted early in the planning process. This publication is also presented as an effort to stimulate interest in learnin

    Renormalization Group Induced Neutrino Mass in Supersymmetry without R-parity

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    We study supersymmetric models without R parity and with universal soft supersymmetry breaking terms. We show that as a result of the renormalization group flow of the parameters, a misalignment between the directions in field space of the down-type Higgs vacuum expectation value vdv_d and of the μ\mu term is always generated. This misalignment induces a mixing between the neutrinos and the neutralinos, resulting in one massive neutrino. By means of a simple approximate analytical expression, we study the dependence on the different parameters that contribute to the misalignment and to mνm_\nu. In large part of the parameter space this effect dominates over the standard one-loop contributions to mνm_\nu; we estimate 1 MeV \lsim m_\nu \lsim 1 GeV. Laboratory, cosmological and astrophysical constraints imply m_\nu \lsim 100 eV. To be phenomenologically viable, these models must be supplemented with some additional mechanism to ensure approximate alignment and to suppress mνm_\nu.Comment: 21 pages, LaTex. Few points clarified, results unchanged. Final version to appear on Physical Review

    Factors Affecting the Course of Resuscitation From Cardiac Arrest With Pulseless Electrical Activity in Children and Adolescents

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    Background: Although in-hospital pediatric cardiac arrests and cardiopulmonary resuscitation occur >15,000/year in the US, few studies have assessed which factors affect the course of resuscitation in these patients. We investigated transitions from Pulseless Electrical Activity (PEA) to Ventricular Fibrillation/pulseless Ventricular Tachycardia (VF/pVT), Return of Spontaneous Circulation (ROSC) and recurrences from ROSC to PEA in children and adolescents with in-hospital cardiac arrest. Methods: Episodes of cardiac arrest at the Children's Hospital of Philadelphia were prospectively registered. Defibrillators that recorded chest compression depth/rate and ventilation rate were applied. CPR variables, patient characteristics and etiology, and dynamic factors (e.g. the proportion of time spent in PEA or ROSC) were entered as time-varying covariates for the transition intensities under study. Results: In 67 episodes of CPR in 59 patients (median age 15 years) with cardiac arrest, there were 52 transitions from PEA to ROSC, 22 transitions from PEA to VF/pVT, and 23 recurrences of PEA from ROSC. Except for a nearly significant effect of mean compression depth beyond a threshold of 5.7 cm, only dynamic factors that evolved during CPR favored a transition from PEA to ROSC. The latter included a lower proportion of PEA over the last 5 min and a higher proportion of ROSC over the last 5 min. Factors associated with PEA to VF/pVT development were age, weight, the proportion spent in VF/pVT or PEA the last 5 min, and the general transition intensity, while PEA recurrence from ROSC only depended on the general transition intensity. Conclusion: The clinical course during pediatric cardiac arrest was mainly influenced by dynamic factors associated with time in PEA and ROSC. Transitions from PEA to ROSC seemed to be favored by deeper compressions.publishedVersio
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