337 research outputs found
Why don't clumps of cirrus dust gravitationally collapse?
We consider the Herschel-Planck infrared observations of presumed
condensations of interstellar material at a measured temperature of
approximately 14 K (Juvela et al., 2012), the triple point temperature of
hydrogen. The standard picture is challenged that the material is cirrus-like
clouds of ceramic dust responsible for Halo extinction of cosmological sources
(Finkbeiner, Davis, and Schlegel 1999). Why would such dust clouds not collapse
gravitationally to a point on a gravitational free-fall time scale of
years? Why do the particles not collide and stick together, as is fundamental
to the theory of planet formation (Blum 2004; Blum and Wurm, 2008) in pre-solar
accretion discs? Evidence from 3.3 m and UIB emissions as well as ERE
(extended red emission) data point to the dominance of PAH-type macromolecules
for cirrus dust, but such fractal dust will not spin in the manner of rigid
grains (Draine & Lazarian, 1998). IRAS dust clouds examined by Herschel-Planck
are easily understood as dark matter Proto-Globular-star-Cluster (PGC) clumps
of primordial gas planets, as predicted by Gibson (1996) and observed by Schild
(1996).Comment: 8 pages, 2 figures, Conference FQMT'1
Evolution of primordial planets in relation to the cosmological origin of life
We explore the conditions prevailing in primordial planets in the framework
of the HGD cosmologies as discussed by Gibson and Schild. The initial stages of
condensation of planet-mass H-4He gas clouds in trillion-planet clumps is set
at 300,000 yr (0.3My) following the onset of plasma instabilities when ambient
temperatures were >1000K. Eventual collapse of the planet-cloud into a solid
structure takes place against the background of an expanding universe with
declining ambient temperatures. Stars form from planet mergers within the
clumps and die by supernovae on overeating of planets. For planets produced by
stars, isothermal free fall collapse occurs initially via quasi equilibrium
polytropes until opacity sets in due to molecule and dust formation. The
contracting cooling cloud is a venue for molecule formation and the sequential
condensation of solid particles, starting from mineral grains at high
temperatures to ice particles at lower temperatures, water-ice becomes
thermodynamically stable between 7 and 15 My after the initial onset of
collapse, and contraction to form a solid icy core begins shortly thereafter.
Primordial-clump-planets are separated by ~ 1000 AU, reflecting the high
density of the universe at 30,000 yr. Exchanges of materials, organic molecules
and evolving templates readily occur, providing optimal conditions for an
initial origin of life in hot primordial gas planet water cores when adequately
fertilized by stardust. The condensation of solid molecular hydrogen as an
extended outer crust takes place much later in the collapse history of the
protoplanet. When the object has shrunk to several times the radius of Jupiter,
the hydrogen partial pressure exceeds the saturation vapour pressure of solid
hydrogen at the ambient temperature and condensation occurs.Comment: 14 pages 7 figures SPIE Conference 7819 Instruments, Methods, and
Missions for Astrobiology XIII Proceedings, Aug 3-5, 2010, San Diego, Ed.
Richard B. Hoove
Detecting and Mitigating Denial-of-Service Attacks on Voice over IP Networks
Voice over IP (VoIP) is more susceptible to Denial of Service attacks than traditional data traffic, due to the former's low tolerance to delay and jitter. We describe the design of our VoIP Vulnerability Assessment Tool (VVAT) with which we demonstrate vulnerabilities to DoS attacks inherent in many of the popular VoIP applications available today. In our threat model we assume an adversary who is not a network administrator, nor has direct control of the channel and key VoIP elements. His aim is to degrade his victim's QoS without giving away his presence by making his attack look like a normal network degradation. Even black-boxed, applications like Skype that use proprietary protocols show poor performance under specially crafted DoS attacks to its media stream. Finally we show how securing Skype relays not only preserves many of its useful features such as seamless traversal of firewalls but also protects its users from DoS attacks such as recording of conversations and disruption of voice quality. We also present our experiences using virtualization to protect VoIP applications from 'insider attacks'.
Our contribution is two fold we: 1) Outline a threat model for VoIP, incorporating our attack models in an open-source network simulator/emulator allowing VoIP vendors to check their software for vulnerabilities in a controlled environment before releasing it. 2) We present two promising approaches for protecting the confidentiality, availability and authentication of VoIP Services
Concept for a Low-Cost, High-Efficiency Precipitation Radar System Based on Ferroelectric Reflectarray Antenna
This work proposes a concept on a novel scanning phased array, based on thin film ferroelectric phase shifters, for an X-band precipitation monostatic radar
Recommended from our members
Low-Cost, Low Fidelity Meat Model to Teach Ultrasound Guided Nerve Blocks
Audience: The target audience of this workshop is emergency medicine residents; however, it is appropriate for all level of learners from medical students to faculty.
Introduction: Pain control is a major focus in the emergency department. Regional anesthesia is a rapidly growing alternative to opioid analgesia or procedural sedation. Nerve blocks are useful in many procedures and are relevant to some of our most common chief complaints. Ultrasound guided regional anesthesia has been shown to be highly successful with minimal complications, and has been shown to reduce the need for supplemental anesthesia such as sedation and narcotics.1 Ultrasound guidance both decreases complications and increases success rate of nerve blocks.2 We provide a simple format for learning relatively safe and technically easy ultrasound guided nerve block techniques. Meat models provide realistic and superior tactilesensation, sono-anatomy, and injection resistance compared to homemade or commercial gel models. Meat and tendons for models are inexpensive and universally available.
Objectives: Upon completion of this workshop, learners will be able to: 1) Describe the risks and benefits of ultrasound guided nerve blocks. 2) Choose the appropriate nerve to block based on the area that needs anesthesia. 3) Display proficiency in performing an ultrasound guided nerve block on meat models. 4) Verbalize confidence in successfully performing ultrasound guided regional anesthesia. By successfullymeeting these objectives, we aim to improve learner confidence and clinical ability in performing ultrasound guided nerve blocks.
Methods: This module consists of a short introductory lecture followed by small group practicums. Learners will rotate through this workshop in groups of four. Each rotation will require about 30 minutes. The instructor will demonstrate appropriate technique for ultrasound guided nerve block using the prepared meat model. Learners will then practice the in-plane ultrasound guided nerve block techniqu
Autoreactivity to Glucose Regulated Protein 78 Links Emphysema and Osteoporosis in Smokers
Rationale: Emphysema and osteoporosis are epidemiologically associated diseases of cigarette smokers. The causal mechanism(s) linking these illnesses is unknown. We hypothesized autoimmune responses may be involved in both disorders. Objectives: To discover an antigen-specific autoimmune response associated with both emphysema and osteoporosis among smokers. Methods: Replicate nonbiased discovery assays indicated that autoimmunity to glucose regulated protein 78 (GRP78), an endoplasmic reticulum chaperone and cell surface signaling receptor, is present in many smokers. Subject assessments included spirometry, chest CT scans, dual x-ray absorptiometry, and immunoblots for anti-GRP78 IgG. Anti-GRP78 autoantibodies were isolated from patient plasma by affinity chromatography, leukocyte functions assessed by flow cytometry, and soluble metabolites and mediators measured by immunoassays. Measurements and Main Results Circulating anti-GRP78 IgG autoantibodies were detected in plasma specimens from 86 (32%) of the 265 smoking subjects. Anti-GRP78 autoantibodies were singularly prevalent among subjects with radiographic emphysema (OR 3.1, 95%CI 1.7–5.7, p = 0.003). Anti-GRP78 autoantibodies were also associated with osteoporosis (OR 4.7, 95%CI 1.7–13.3, p = 0.002), and increased circulating bone metabolites (p = 0.006). Among emphysematous subjects, GRP78 protein was an autoantigen of CD4 T-cells, stimulating lymphocyte proliferation (p = 0.0002) and IFN-gamma production (p = 0.03). Patient-derived anti-GRP78 autoantibodies had avidities for osteoclasts and macrophages, and increased macrophage NFkB phosphorylation (p = 0.005) and productions of IL-8, CCL-2, and MMP9 (p = 0.005, 0.007, 0.03, respectively). Conclusions: Humoral and cellular GRP78 autoimmune responses in smokers have numerous biologically-relevant pro-inflammatory and other deleterious actions, and are associated with emphysema and osteoporosis. These findings may have relevance for the pathogenesis of smoking-associated diseases, and development of biomarker immunoassays and/or novel treatments for these disorders
- …