897 research outputs found
Correlation functions and emission time sequence of light charged particles from projectile-like fragment source in E/A = 44 and 77 MeV 40Ar + 27Al collisions
Two-particle correlation functions, involving protons, deuterons, tritons,
and alpha-particles, have been measured at very forward angles (0.7 deg <
theta_lab < 7 deg), in order to study projectile-like fragment (PLF) emission
in E/A = 44 and 77 MeV 40Ar + 27Al collisions. Peaks, originating from
resonance decays, are larger at E/A = 44 than at 77 MeV. This reflects the
larger relative importance of independently emitted light particles, as
compared to two-particle decay from unstable fragments, at the higher beam
energy. The time sequence of the light charged particles, emitted from the PLF,
has been deduced from particle-velocity-gated correlation functions (discarding
the contribution from resonance decays). Alpha-particles are found to have an
average emission time shorter than protons but longer than tritons and
deuterons.Comment: 18 pages, 5 figures, submitted to Nuclear Physics
Analysis of charged particle emission sources and coalescence in E/A = 61 MeV Ar + Al, Sn and Sn collisions
Single-particle kinetic energy spectra and two-particle small angle
correlations of protons (), deuterons () and tritons () have been
measured simultaneously in 61A MeV Ar + Al, Sn and
Sn collisions. Characteristics of the emission sources have been
derived from a ``source identification plot'' (--
plot), constructed from the single-particle invariant spectra, and compared to
the complementary results from two-particle correlation functions. Furthermore,
the source identification plot has been used to determine the conditions when
the coalescence mechanism can be applied for composite particles. In our data,
this is the case only for the Ar + Al reaction, where , and are
found to originate from a common source of emission (from the overlap region
between target and projectile). In this case, the coalescence model parameter,
-- the radius of the complex particle emission source in momentum
space, has been analyzed.Comment: 20 pages, 5 figures, submitted to Nuclear Physics
The Role of Phase Space in Complex Fragment Emission from Low to Intermediate Energies
The experimental emission probabilities of complex fragments by low energy
compound nuclei and their dependence upon energy and atomic number are compared
to the transition state rates. Intermediate-mass-fragment multiplicity
distributions for a variety of reactions at intermediate energies are shown to
be binomial and thus reducible at all measured transverse energies. From these
distributions a single binary event probability can be extracted which has a
thermal dependence. A strong thermal signature is also found in the charge
distributions. The n-fold charge distributions are reducible to the 1-fold
charge distributions through a simple scaling dictated by fold number and
charge conservation.Comment: 15 pages, TeX type, psfig, also available at
http://csa5.lbl.gov/moretto/ps/brazil.ps, to appear in Proceedings of the 1st
International Conference on Nuclear Dynamics at Long and Short Distances,
April 8-12, 1996, Angra dos Reis, Brazi
Correlations and Characterization of Emitting Sources
Dynamical and thermal characterizations of excited nuclear systems produced
during the collisions between two heavy ions at intermediate incident energies
are presented by means of a review of experimental and theoretical work
performed in the last two decades. Intensity interferometry, applied to both
charged particles (light particles and intermediate mass fragments) and to
uncharged radiation (gamma rays and neutrons) has provided relevant information
about the space-time properties of nuclear reactions. The volume, lifetime,
density and relative chronology of particle emission from decaying nuclear
sources has been extensively explored and has provided valuable information
about the dynamics of heavy-ion collisions. Similar correlation techniques
applied to coincidences between light particles and complex fragments are also
presented as a tool to determine the internal excitation energy of excited
primary fragments as it appears in secondary-decay phenomena.Comment: To appear on Euorpean Physics Journal A as part of the Topical Volume
"Dynamics and Thermodynamics with Nuclear Degrees of Freedom
The complement: a solution to liquid drop finite size effects in phase transitions
The effects of the finite size of a liquid drop undergoing a phase transition
are described in terms of the complement, the largest (but still mesoscopic)
drop representing the liquid in equilibrium with the vapor. Vapor cluster
concentrations, pressure and density from fixed mean density lattice gas
(Ising) model calculations are explained in terms of the complement. Accounting
for this finite size effect is key to determining the infinite nuclear matter
phase diagram from experimental data.Comment: Four two column pages, four figures, two tables; accepted for
publication in PR
From upper limits to detection : continuous gravitational waves in the advanced detector era
This thesis concerns continuous gravitational wave signals from non-axisymmetric neutron stars and ground-based interferometric detectors. These detectors are currently being upgraded and this thesis explores relevant issues and methods to prepare for the advanced detector era. A study into sensitivity dependence on the addition of a southern hemisphere detector for a targeted continuous wave search is first presented. Next, we study the effect of close and/or high velocity neutron stars on the ability of a blind, all-sky search to make a detection. Initial results from a narrowband search for signals from the Crab Pulsar and a blind hardware injected signal are then presented. Finally, we describe the development and initial implementation of a large-scale mock data challenge designed to test current continuous wave algorithms to explore various issues before we enter the advanced detector era.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Novel tau filament fold in chronic traumatic encephalopathy encloses hydrophobic molecules
Chronic traumatic encephalopathy (CTE) is a neurodegenerative tauopathy that is associated with repetitive head impacts or exposure to blast waves. First described as punch-drunk syndrome and dementia pugilistica in retired boxers1-3, CTE has since been identified in former participants of other contact sports, ex-military personnel and after physical abuse4-7. No disease-modifying therapies currently exist, and diagnosis requires an autopsy. CTE is defined by an abundance of hyperphosphorylated tau protein in neurons, astrocytes and cell processes around blood vessels8,9. This, together with the accumulation of tau inclusions in cortical layers II and III, distinguishes CTE from Alzheimer's disease and other tauopathies10,11. However, the morphologies of tau filaments in CTE and the mechanisms by which brain trauma can lead to their formation are unknown. Here we determine the structures of tau filaments from the brains of three individuals with CTE at resolutions down to 2.3 Å, using cryo-electron microscopy. We show that filament structures are identical in the three cases but are distinct from those of Alzheimer's and Pick's diseases, and from those formed in vitro12-15. Similar to Alzheimer's disease12,14,16-18, all six brain tau isoforms assemble into filaments in CTE, and residues K274-R379 of three-repeat tau and S305-R379 of four-repeat tau form the ordered core of two identical C-shaped protofilaments. However, a different conformation of the β-helix region creates a hydrophobic cavity that is absent in tau filaments from the brains of patients with Alzheimer's disease. This cavity encloses an additional density that is not connected to tau, which suggests that the incorporation of cofactors may have a role in tau aggregation in CTE. Moreover, filaments in CTE have distinct protofilament interfaces to those of Alzheimer's disease. Our structures provide a unifying neuropathological criterion for CTE, and support the hypothesis that the formation and propagation of distinct conformers of assembled tau underlie different neurodegenerative diseases
Human resource strategies of Chinese state crewing agencies with special reference to labour export and the experience of Chinese seafarers
The Chinese shipping industry is one of the fastest developing sectors in the Chinese economy. However, few studies have explored the changes within it, especially concerning its human resource element - seafarers - and the newly formed crewing agencies through which they are employed. This research seeks to explore the contemporary experience of Chinese seafarers and especially how this is impacted by the management strategies of Chinese crewing agencies. In doing so, it contributes to debates about changes in Chinese society - that is, whether the economic reform has led to a new market economy in China. The idea of the emergence of a modernized, free Chinese seafarer labour market is critically examined through research into the employment and labour supply strategies of two ship crewing agencies, which have been reformed to different degrees, and the experience of the seafarers who work for them. The research utilises qualitative methods, with twenty-two managers and fifty seafarers being interviewed extensively, supplemented by documentary research. It seeks to explain why China's seafaring labour export is far lower than people have expected. It is seen that it is difficult to characterise China's seafarer labour market as a free market. The state has limited the liberalization of the market by granting foreign manning qualification to less than sixty state-owned crewing agencies. It is seen that institutions at higher levels still intervene in the operation of the agencies, with their management consequently showing a lack of market orientation to different extents, which constrains the development of China's labour export. It is also difficult to characterise the movement of Chinese seafarers in the labour market as free movement. The argument that Chinese economic reform leads to the transformation of Chinese seafarers into freelancers, which implies a substantial increase of seafarer export due to the attractiveness of working in foreign shipping companies, is too simplistic. In addition, the wages of Chinese seafarers working in the global labour market are lower than the international benchmark rates and are not necessarily higher than the payments by domestic shipping companies. This weakens the willingness of Chinese seafarers to work in foreign shipping companies.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
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Phase coexistence in multifragmentation?
The charge (Z) distributions from intermediate energy heavy-ion reactions depend upon the multiplicity {eta} of intermediate mass fragments through a factor of the form e{sup {minus}cnZ}. Experimentally c starts from zero at low values of the transverse energy E{sub t} and reaches a saturation value at high E{sub t}. In a liquid-gas phase diagram, c = 0 for the saturated vapor, while c {gt} 0 for the unsaturated vapor. It is suggested that in the c {approx} 0 regime the source evaporates down to a sizable remnant, while for c {gt} 0 the source vaporizes completely. Percolation of a finite system portrays a behavior similar to that observed experimentally
Quantum corrections for pion correlations involving resonance decays
A method is presented to include quantum corrections into the calculation of
two-pion correlations for the case where particles originate from resonance
decays. The technique uses classical information regarding the space-time
points at which resonances are created. By evaluating a simple thermal model,
the method is compared to semiclassical techniques that assume exponential
decaying resonances moving along classical trajectories. Significant
improvements are noted when the resonance widths are broad as compared to the
temperature.Comment: 9 pages, 4 figure
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