12,789 research outputs found
A 233 km Tunnel for Lepton and Hadron Colliders
A decade ago, a cost analysis was conducted to bore a 233 km circumference
Very Large Hadron Collider (VLHC) tunnel passing through Fermilab. Here we
outline implementations of , , and collider
rings in this tunnel using recent technological innovations. The 240 and 500
GeV colliders employ Crab Waist Crossings, ultra low emittance damped
bunches, short vertical IP focal lengths, superconducting RF, and low
coercivity, grain oriented silicon steel/concrete dipoles. Some details are
also provided for a high luminosity 240 GeV collider and 1.75 TeV
muon accelerator in a Fermilab site filler tunnel. The 40 TeV
collider uses the high intensity Fermilab source, exploits high cross
sections for production of high mass states, and uses 2 Tesla ultra
low carbon steel/YBCO superconducting magnets run with liquid neon. The 35 TeV
muon ring ramps the 2 Tesla superconducting magnets at 9 Hz every 0.4 seconds,
uses 250 GV of superconducting RF to accelerate muons from 1.75 to 17.5 TeV in
63 orbits with 71% survival, and mitigates neutrino radiation with phase
shifting, roller coaster motion in a FODO lattice.Comment: LaTex, 6 pages, 1 figure, Advanced Accelerator Concepts Workshop,
Austin, TX, 10-15 June 201
Nonlocal hydrodynamic influence on the dynamic contact angle: Slip models versus experiment
Experiments reported by Blake et al. [Phys. Fluids. 11, 1995 (1999)] suggest that the dynamic contact angle formed between the free surface of a liquid and a moving solid boundary at a fixed contact-line speed depends on the flow field/geometry near the moving contact line. The present paper examines quantitatively whether or not it is possible to attribute this effect to bending of the free surface due to hydrodynamic stresses acting upon it and hence interpret the results in terms of the so-called ``apparent'' contact angle. It is shown that this is not the case. Numerical analysis of the problem demonstrates that, at the spatial
resolution reported in the experiments, the variations of the ``apparent'' contact angle (defined in two different ways) caused by variations in the flow field, at a fixed contact-line speed, are too small to account for the observed effect. The results clearly indicate that the actual (macroscopic) dynamic contact angle, i.e.\ the one used in fluid mechanics as a boundary condition for the equation determining the free surface shape, must be regarded as dependent not only on the contact-line speed but also on the flow field/geometry in the vicinity of the moving contact line
Fronto-striatal cognitive deficits at different stages of Parkinson's disease
Groups of patients with idiopathic Parkinson's disease, either medicated or unmedicated, were compared with matched groups of normal controls on a computerized battery previously shown to be sensitive to frontal lobe dysfunction, including tests of planning, spatial working memory and attentional set-shifting. In a series of problems based on the 'Tower of London' test, medicated patients with Parkinson's disease were shown to be impaired in the amount of time spent thinking about (planning) the solution to each problem. Additionally, an impairment in terms of the accuracy of the solution produced on this test was only evident in those patients with more severe clinical symptoms and was accompanied by deficits in an associated test of spatial short-term memory. Medicated patients with both mild and severe clinical symptoms were also impaired on a related test of spatial working memory. In contrast, a group of patients who were unmedicated and 'early in the course' of the disease were unimpaired in all three of these tests. However, all three Parkinson's disease groups were impaired in the test of attentional set-shifting ability, although unimpaired in a test of pattern recognition which is insensitive to frontal lobe damage. These data are compared with those previously published from a group of young neurosurgical patients with localized excisions of the frontal lobes and are discussed in terms of the specific nature of the cognitive deficit at different stages of Parkinson's disease
Theoretical Analysis of the Relative Impact of Obesity on Hemodynamic Stability During Acute Hemorrhagic Shock
Background: Evidence suggests that morbid obesity may be an independent risk factor for adverse outcomes in patients with traumatic injuries.
Objectives: In this study, a theoretic analysis using a derivation of the Guyton model of cardiovascular physiology examines the expected impact of obesity on hemodynamic changes in Mean Arterial Pressure (MAP) and Cardiac Output (CO) during Hemorrhagic Shock (HS).
Patients and Methods: Computer simulation studies were used to predict the relative impact of increasing Body Mass Index (BMI) on global hemodynamic parameters during HS. The analytic procedure involved recreating physiologic conditions associated with changing BMI for a virtual subject in an In Silico environment. The model was validated for the known effect of a BMI of 30 on iliofemoral venous pressures. Then, the relative effect of changing BMI on the outcome of target cardiovascular parameters was examined during simulated acute loss of blood volume in class II hemorrhage. The percent changes in these parameters were compared between the virtual nonobese and obese subjects. Model parameter values are derived from known population distributions, producing simulation outputs that can be used in a deductive systems analysis assessment rather than traditional frequentist statistical methodologies.
Results: In hemorrhage simulation, moderate increases in BMI were found to produce greater decreases in MAP and CO compared to the normal subject. During HS, the virtual obese subject had 42% and 44% greater falls in CO and MAP, respectively, compared to the nonobese subject. Systems analysis of the model revealed that an increase in resistance to venous return due to changes in intra-abdominal pressure resulting from obesity was the critical mechanism responsible for the differences.
Conclusions: This study suggests that obese patients in HS may have a higher risk of hemodynamic instability compared to their nonobese counterparts primarily due to obesity-induced increases in intra-abdominal pressure resulting in reduced venous return
High-performance reactionless scan mechanism
A high-performance reactionless scan mirror mechanism was developed for space applications to provide thermal images of the Earth. The design incorporates a unique mechanical means of providing reactionless operation that also minimizes weight, mechanical resonance operation to minimize power, combined use of a single optical encoder to sense coarse and fine angular position, and a new kinematic mount of the mirror. A flex pivot hardware failure and current project status are discussed
A structural evaluation of the tungsten isotopes via thermal neutron capture
Total radiative thermal neutron-capture -ray cross sections for the
W isotopes were measured using guided neutron beams from
the Budapest Research Reactor to induce prompt and delayed rays from
elemental and isotopically-enriched tungsten targets. These cross sections were
determined from the sum of measured -ray cross sections feeding the
ground state from low-lying levels below a cutoff energy, E, where
the level scheme is completely known, and continuum rays from levels
above E, calculated using the Monte Carlo statistical-decay code
DICEBOX. The new cross sections determined in this work for the tungsten
nuclides are: b and
b;
b and b; b and
b; and,
b and b. These results are consistent with
earlier measurements in the literature. The W cross section was also
independently confirmed from an activation measurement, following the decay of
W, yielding values for that are consistent
with our prompt -ray measurement. The cross-section measurements were
found to be insensitive to choice of level density or photon strength model,
and only weakly dependent on E. Total radiative-capture widths
calculated with DICEBOX showed much greater model dependence, however, the
recommended values could be reproduced with selected model choices. The decay
schemes for all tungsten isotopes were improved in these analyses.Comment: 25 pages, 15 figures, 15 table
Structural basis for mechanotransduction in a potassium-dependent mechanosensitive ion channel
Mechanosensitive channels of small conductance, found in many living organisms, open under elevated membrane tension and thus play crucial roles in biological response to mechanical stress. Amongst these channels, MscK is unique in that its activation also requires external potassium ions. To better understand this dual gating mechanism by force and ligand, we elucidate distinct structures of MscK along the gating cycle using cryo-electron microscopy. The heptameric channel comprises three layers: a cytoplasmic domain, a periplasmic gating ring, and a markedly curved transmembrane domain that flattens and expands upon channel opening, which is accompanied by dilation of the periplasmic ring. Furthermore, our results support a potentially unifying mechanotransduction mechanism in ion channels depicted as flattening and expansion of the transmembrane domain
Effect of EMIC waves on relativistic and ultrarelativistic electron populations: Ground-based and Van Allen Probes observations
Abstract We study the effect of electromagnetic ion cyclotron (EMIC) waves on the loss and pitch angle scattering of relativistic and ultrarelativistic electrons during the recovery phase of a moderate geomagnetic storm on 11 October 2012. The EMIC wave activity was observed in situ on the Van Allen Probes and conjugately on the ground across the Canadian Array for Real-time Investigations of Magnetic Activity throughout an extended 18 h interval. However, neither enhanced precipitation of \u3e0.7 MeV electrons nor reductions in Van Allen Probe 90° pitch angle ultrarelativistic electron flux were observed. Computed radiation belt electron pitch angle diffusion rates demonstrate that rapid pitch angle diffusion is confined to low pitch angles and cannot reach 90°. For the first time, from both observational and modeling perspectives, we show evidence of EMIC waves triggering ultrarelativistic (~2-8 MeV) electron loss but which is confined to pitch angles below around 45° and not affecting the core distribution. Key Points EMIC wave activity is not associated with precipitation of MeV electrons EMIC waves do not deplete the ultra-relativistic belt down to 90° EMIC waves cause loss of low pitch angle electrons with energies ~2-8 MeV
Quantum Gravity Effects in Black Holes at the LHC
We study possible back-reaction and quantum gravity effects in the
evaporation of black holes which could be produced at the LHC through a
modification of the Hawking emission. The corrections are phenomenologically
taken into account by employing a modified relation between the black hole mass
and temperature. The usual assumption that black holes explode around TeV
is also released, and the evaporation process is extended to (possibly much)
smaller final masses. We show that these effects could be observable for black
holes produced with a relatively large mass and should therefore be taken into
account when simulating micro-black hole events for the experiments planned at
the LHC.Comment: 14 pages, 8 figures, extended version of hep-ph/0601243 with new
analysis of final products, final version accepted for publication in J.
Phys.
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