4,191 research outputs found
Primordial Black Holes, Hawking Radiation and the Early Universe
The 511 keV gamma emission from the galactic core may originate from a high
concentration () of primordial black holes (PBHs) in the core
each of whose Hawking radiation includes positrons per second.
The PBHs we consider are taken as near the lightest with longevity greater than
the age of the universe (mass kg; Schwarzschild radius
fm). These PBHs contribute only a small fraction of cold dark matter,
. This speculative hypothesis, if confirmed implies
the simultaneous discovery of Hawking radiation and an early universe phase
transition.Comment: 4 Page
Phase 1 Trial of Vaccination with Autologous Tumor Cells and Antisense Directed Against the Insulin Growth Factor Type 1 Receptor (IGF-1R AS ODN) in Patients with Recurrent Glioblastoma
Background: Extending a previous Phase I study, we report the results of a second Phase I autologous tumor cell vaccination trial for patients with recurrent glioblastomas (IND 14379-101, NCT01550523).
Methods: Following surgery, subjects were treated by 24 hour implantation in the rectus sheath of ten biodiffusion chambers containing irradiated autologous tumor cells and IGF-1R AS ODN with the objective of stimulating tumor immunity. Patients were monitored for safety, clinical and radiographic as well as immune responses.
Results: There were no Grade 3 toxicities related to protocol treatment and overall median survival from initial diagnosis was 91.4 weeks. Two protocol survival cohorts with median survivals of 48.2 and 10 weeks were identified and predicted by our pre-treatment assessments of immune function, corroborated by post-vaccination pro-inflammatory cytokine profiles. Longer survival subjects had imaging findings including transient elevations in cerebral blood volume (rCBV) and sustained elevations of apparent diffusion coefficient (ADC) interpreted as transient hyperemia and cell loss.
Conclusions: The vaccine paradigm was well-tolerated with a favorable median survival. Our data support this as a novel treatment paradigm that promotes anti-tumor immunity
Payload/orbiter contamination control requirement study: Computer interface
A preliminary assessment of the computer interface requirements of the Spacelab configuration contamination computer model was conducted to determine the compatibility of the program, as presently formatted, with the computer facilities at MSFC. The necessary Spacelab model modifications are pointed out. The MSFC computer facilities and their future plans are described, and characteristics of the various computers as to availability and suitability for processing the contamination program are discussed. A listing of the CDC 6000 series and UNIVAC 1108 characteristics is presented so that programming requirements can be compared directly and differences noted
The Milky Way as a Kiloparsec-Scale Axionscope
Very high energy gamma-rays are expected to be absorbed by the extragalactic
background light over cosmological distances via the process of
electron-positron pair production. Recent observations of cosmologically
distant gamma-ray emitters by ground based gamma-ray telescopes have, however,
revealed a surprising degree of transparency of the universe to very high
energy photons. One possible mechanism to explain this observation is the
oscillation between photons and axion-like-particles (ALPs). Here we explore
this possibility further, focusing on photon-ALP conversion in the magnetic
fields in and around gamma-ray sources and in the magnetic field of the Milky
Way, where some fraction of the ALP flux is converted back into photons. We
show that this mechanism can be efficient in allowed regions of the ALP
parameter space, as well as in typical configurations of the Galactic Magnetic
Field. As case examples, we consider the spectrum observed from two HESS
sources: 1ES1101-232 at redshift z=0.186 and H 2356-309 at z=0.165. We also
discuss features of this scenario which could be used to distinguish it from
standard or other exotic models.Comment: 7 pages, 4 figures. Matches published versio
Pierre Auger Data, Photons, and Top-Down Cosmic Ray Models
We consider the ultra-high energy cosmic ray (UHECR) spectrum as measured by
the Pierre Auger Observatory. Top-down models for the origin of UHECRs predict
an increasing photon component at energies above about eV. Here we
present a simple prescription to compare the Auger data with a prediction
assuming a pure proton component or a prediction assuming a changing primary
component appropriate for a top-down model. We find that the UHECR spectrum
predicted in top-down models is a good fit to the Auger data. Eventually, Auger
will measure a composition-independent spectrum and will be capable of either
confirming or excluding the quantity of photons predicted in top-down models.Comment: 8 pages, 3 figure
Two photon annihilation of Kaluza-Klein dark matter
We investigate the fermionic one-loop cross section for the two photon
annihilation of Kaluza-Klein (KK) dark matter particles in a model of universal
extra dimensions (UED). This process gives a nearly mono-energetic gamma-ray
line with energy equal to the KK dark matter particle mass. We find that the
cross section is large enough that if a continuum signature is detected, the
energy distribution of gamma-rays should end at the particle mass with a peak
that is visible for an energy resolution of the detector at the percent level.
This would give an unmistakable signature of a dark matter origin of the
gamma-rays, and a unique determination of the dark matter particle mass, which
in the case studied should be around 800 GeV. Unlike the situation for
supersymmetric models where the two-gamma peak may or may not be visible
depending on parameters, this feature seems to be quite robust in UED models,
and should be similar in other models where annihilation into fermions is not
helicity suppressed. The observability of the signal still depends on largely
unknown astrophysical parameters related to the structure of the dark matter
halo. If the dark matter near the galactic center is adiabatically contracted
by the central star cluster, or if the dark matter halo has substructure
surviving tidal effects, prospects for detection look promising.Comment: 17 pages, 3 figures; slightly revised versio
Temperature effects on laminated glass at high rate
The load bearing capacity of a laminated glass pane changes with temperature. In blast protection, laminated glass panes with a Polyvinyl Butyral (PVB) interlayer are usually employed. The post-crack response of the laminated pane is determined by the interlayer material response and its bond to the glass plies. An experimental study has been performed to determine the effects of temperature on the post cracked response of laminated glass at a test rate of 1 m/s for PVB thicknesses of 0.76 mm, 1.52 mm and 2.28 mm. Tensile tests were carried out on single cracked and randomly cracked samples in a temperature range of 0 °C–60 °C. Photoelasticity observation and high speed video recording were used to capture the delamination in the single cracked tests. Competing mechanisms of PVB compliance and the adhesion between the glass and PVB, were revealed. The adhesion showed an increase at lower temperatures, but the compliance of the PVB interlayer was reduced. Based on the interlayer thickness range tested, the post-crack response of laminated glass is shown to be thickness dependent
A study on the bending of laminated glass under blast loading
Background: The bending behaviour of laminated glass plays an important role in determining its overall response to blast loading. It is costly and difficult to characterise the bending behaviour by carrying out full-scale blast tests, therefore an alternative method is required. Objective: The objective of this study is to understand the response of laminated glass under high-rate bending in the laboratory at rates representative of blast loading. Methods: In this paper a novel testing method is presented in which laminated glass strips of 700 mm long by 60 mm wide are tested up to speeds of 10 m/s in the laboratory. The laminated glass is accelerated to speeds comparable to blast loading and then brought to rest at its edges to mimic impulsive blast loading conditions. Different interlayer thickness, impact speeds, and boundary conditions were explored. Additionally, modelling methods were used to study the flexural rigidity of post-cracked laminated glass. Results: From the experiments it was found that the interlayer thickness plays a key role in determining whether the dominant failure mechanism is de-bonding of interlayer from the glass or interlayer tearing. In addition, it was found that by allowing the frame to bend under loading, the laminated glass can carry greater loads without failure. Finally, an iterative method was used to quantify the flexural rigidity of post-cracked laminated glass depending on the speed of travel. This is a novel finding as it is usually assumed that laminated glass behaves like a membrane in the post-cracked phase of the response. Conclusion: In modelling and design of laminated glass structures under blast loading, post-crack flexural rigidity must be taken into account. Additionally, having novel frame designs to add further load bearing capacity to the framing members, plays a key role in reducing the load intensity on the laminated glass structure
- …