1,756 research outputs found
The applicability of causal dissipative hydrodynamics to relativistic heavy ion collisions
We utilize nonequilibrium covariant transport theory to determine the region
of validity of causal Israel-Stewart dissipative hydrodynamics (IS) and
Navier-Stokes theory (NS) for relativistic heavy ion physics applications. A
massless ideal gas with 2->2 interactions is considered in a 0+1D Bjorken
scenario, appropriate for the early longitudinal expansion stage of the
collision. In the scale invariant case of a constant shear viscosity to entropy
density ratio eta/s ~ const, we find that Israel-Stewart theory is 10% accurate
in calculating dissipative effects if initially the expansion timescale exceeds
half the transport mean free path tau0/lambda0 > ~2. The same accuracy with
Navier-Stokes requires three times larger tau0/lambda0 > ~6. For dynamics
driven by a constant cross section, on the other hand, about 50% larger
tau0/lambda0 > ~3 (IS) and ~9 (NS) are needed. For typical applications at RHIC
energies s_{NN}**(1/2) ~ 100-200 GeV, these limits imply that even the
Israel-Stewart approach becomes marginal when eta/s > ~0.15. In addition, we
find that the 'naive' approximation to Israel-Stewart theory, which neglects
products of gradients and dissipative quantities, has an even smaller range of
applicability than Navier-Stokes. We also obtain analytic Israel-Stewart and
Navier-Stokes solutions in 0+1D, and present further tests for numerical
dissipative hydrodynamics codes in 1+1, 2+1, and 3+1D based on generalized
conservation laws.Comment: 30 pages, 26 EPS figures, revtex stylefil
A low-power, radiation-hard gigabit serializer for use in the CMS electromagnetic calorimeter
An integrated fiber-optic bit serializer and VCSEL driver has been constructed in radiation-hard complementary heterostructure GaAs FET (CHFET) technology. The serializer, which converts 20 parallel inputs into a high-speed serial output, consumes 60 mW at nominal supply voltage when operating at the Large Hadron Collider word rate of 40 MHz (0.8-GB/s serial rate). The integrated driver directly drives a VCSEL and provides 10-mA switched current and 5 mA of prebias. The complete digital optical link thus consumes 90 mW. (6 refs)
Monolithic Pixel Sensors in Deep-Submicron SOI Technology
Monolithic pixel sensors for charged particle detection and imaging
applications have been designed and fabricated using commercially available,
deep-submicron Silicon-On-Insulator (SOI) processes, which insulate a thin
layer of integrated full CMOS electronics from a high-resistivity substrate by
means of a buried oxide. The substrate is contacted from the electronics layer
through vias etched in the buried oxide, allowing pixel implanting and reverse
biasing. This paper summarizes the performances achieved with a first prototype
manufactured in the OKI 0.15 micrometer FD-SOI process, featuring analog and
digital pixels on a 10 micrometer pitch. The design and preliminary results on
the analog section of a second prototype manufactured in the OKI 0.20
micrometer FD-SOI process are briefly discussed.Comment: Proceedings of the PIXEL 2008 International Workshop, FNAL, Batavia,
IL, 23-26 September 2008. Submitted to JINST - Journal of Instrumentatio
Cross-linguistic study of vocal pathology: perceptual features of spasmodic dysphonia in French-speaking subjects
Clinical characterisation of Spasmodic Dysphonia of the adductor type (SD) in French speakers by Klap and colleagues (1993) appears to differ from that of SD in English. This perceptual analysis aims to describe the phonetic features of French SD. A video of 6 French speakers with SD supplied by Klap and colleagues was analysed for frequency of phonatory breaks, pitch breaks, harshness, creak, breathiness and falsetto voice, rate of production, and quantity of speech output. In contrast to English SD, the French speaking SD patients demonstrated no evidence pitch breaks, but phonatory breaks, harshness and breathiness were prominent features. This verifies the French authors’ (1993) clinical description. These findings suggest that phonetic properties of a specific language may affect the manifestation of pathology in neurogenic voice disorders
港珠澳大橋-香港口岸國際概念設計大賽參賽作品
這是一個港澳珠跨海大橋香港口岸的概念設計,基地位於比鄰香港國際機場的填海人工島上,四下空曠,因為地處飛機起落的航線上,它有嚴格的高度限制。我們的初衷是創造一個地標光塔,它光彩斑斕、形態舞動,無論從陸地還是海上,空中還是山上,看上去它都會成為一個令人過目難忘的香港門戶。This entry to the Hong Kong Boundary Crossing Facilities (HKBCF) International Design Ideas Competition proposes an iconic beacon of dazzling light, colour and geometrical dynamics, visible as a gateway to Hong Kong, from the approach of both directions of the HKZM Bridge, from the air along the flight paths to HK airport, and the hills of Lantau Island and the New Territories.published_or_final_versio
Modularity of gene-regulatory networks revealed in sea-star development
Evidence that conserved developmental gene-regulatory networks can change as a unit during deutersostome evolution emerges from a study published in BMC Biology. This shows that genes consistently expressed in anterior brain patterning in hemichordates and chordates are expressed in a similar spatial pattern in another deuterostome, an asteroid echinoderm (sea star), but in a completely different developmental context (the animal-vegetal axis). This observation has implications for hypotheses on the type of development present in the deuterostome common ancestor
The prognosis of allocentric and egocentric neglect : evidence from clinical scans
We contrasted the neuroanatomical substrates of sub-acute and chronic visuospatial deficits associated with different aspects of unilateral neglect using computed tomography scans acquired as part of routine clinical diagnosis. Voxel-wise statistical analyses were conducted on a group of 160 stroke patients scanned at a sub-acute stage. Lesion-deficit relationships were assessed across the whole brain, separately for grey and white matter. We assessed lesions that were associated with behavioural performance (i) at a sub-acute stage (within 3 months of the stroke) and (ii) at a chronic stage (after 9 months post stroke). Allocentric and egocentric neglect symptoms at the sub-acute stage were associated with lesions to dissociated regions within the frontal lobe, amongst other regions. However the frontal lesions were not associated with neglect at the chronic stage. On the other hand, lesions in the angular gyrus were associated with persistent allocentric neglect. In contrast, lesions within the superior temporal gyrus extending into the supramarginal gyrus, as well as lesions within the basal ganglia and insula, were associated with persistent egocentric neglect. Damage within the temporo-parietal junction was associated with both types of neglect at the sub-acute stage and 9 months later. Furthermore, white matter disconnections resulting from damage along the superior longitudinal fasciculus were associated with both types of neglect and critically related to both sub-acute and chronic deficits. Finally, there was a significant difference in the lesion volume between patients who recovered from neglect and patients with chronic deficits. The findings presented provide evidence that (i) the lesion location and lesion size can be used to successfully predict the outcome of neglect based on clinical CT scans, (ii) lesion location alone can serve as a critical predictor for persistent neglect symptoms, (iii) wide spread lesions are associated with neglect symptoms at the sub-acute stage but only some of these are critical for predicting whether neglect will become a chronic disorder and (iv) the severity of behavioural symptoms can be a useful predictor of recovery in the absence of neuroimaging findings on clinical scans. We discuss the implications for understanding the symptoms of the neglect syndrome, the recovery of function and the use of clinical scans to predict outcome
Study of Spin and Decay-Plane Correlations of W Bosons in the e+e- -> W+W- Process at LEP
Data collected at LEP at centre-of-mass energies \sqrt(s) = 189 - 209 GeV are
used to study correlations of the spin of W bosons using e+e- -> W+W- -> lnqq~
events. Spin correlations are favoured by data, and found to agree with the
Standard Model predictions. In addition, correlations between the W-boson decay
planes are studied in e+e- -> W+W- -> lnqq~ and e+e- -> W+W- -> qq~qq~ events.
Decay-plane correlations, consistent with zero and with the Standard Model
predictions, are measured
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