99 research outputs found
Dibaryons in neutron stars
The effects are studied of H-dibaryons on the structure of neutron stars. It was found that H particles could be present in neutron stars for a wide range of dibaryon masses. The appearance of dibaryons softens the equations of state, lowers the maximum neutron star mass, and affects the transport properties of dense matter. The parameter space is constrained for dibaryons by requiring that a 1.44 solar mass neutron star be gravitationally stable
The final phase of inspiral of neutron stars: realistic equations of state
Coalescing compact star binaries are expected to be among the strongest
sources of gravitational radiation to be seen by laser interferometers. We
present calculations of the final phase of inspiral of equal mass irrotational
neutron star binaries and strange quark star binaries. Six types of equations
of state at zero temperature are used - three realistic nuclear equations of
state of various softness and three different MIT bag models of strange quark
matter. We study the precoalescing stage within the Isenberg-Wilson-Mathews
approximation of general relativity using a multidomain spectral method. The
gravitational-radiation driven evolution of the binary system is approximated
by a sequence of quasi-equilibrium configurations at fixed baryon number and
decreasing separation. We find that the innermost stable circular orbit (ISCO)
is given by an orbital instability for binary strange quark stars and by the
mass-shedding limit for neutron star binaries. The gravitational wave frequency
at the ISCO, which marks the end of the inspiral phase, is found to be around
1100-1460 Hz for two 1.35 solar masses irrotational strange stars described by
the MIT bag model and between 800 Hz and 1230 Hz for neutron stars.Comment: 6 pages, 2 figures, Advances in Space Research, in
press,doi:10.1016/j.asr.2006.09.021, available online www.sciencedirect.com,
paper updated according to the reviewer's suggestions (conclusions unchanged
Entrainment coefficient and effective mass for conduction neutrons in neutron star crust: II Macroscopic treatment
Phenomena such as pulsar frequency glitches are believed to be attributable
to differential rotation of a current of ``free'' superfluid neutrons at
densities above the ``drip'' threshold in the ionic crust of a neutron star.
Such relative flow is shown to be locally describable by adaption of a
canonical two fluid treatment that emphasizes the role of the momentum
covectors constructed by differentiation of action with respect to the
currents, with allowance for stratification whereby the ionic number current
may be conserved even when the ionic charge number Z is altered by beta
processes. It is demonstrated that the gauge freedom to make different choices
of the chemical basis determining which neutrons are counted as ``free'' does
not affect their ``superfluid'' momentum covector, which must locally have the
form of a gradient (though it does affect the ``normal'' momentum covector
characterising the protons and those neutrons that are considered to be
``confined'' in the nuclei). It is shown how the effect of ``entrainment''
(whereby the momentum directions deviate from those of the currents) is
controlled by the (gauge independent) mobility coefficient K, estimated in
recent microscopical quantum mechanical investigations, which suggest that the
corresponding (gauge dependent) ``effective mass'' m* of the free neutrons can
become very large in some layers. The relation between this treatment of the
crust layers and related work (using different definitions of ``effective
mass'') intended for the deeper core layers is discussed.Comment: 21 pages Latex. Part II of article whose Part I (Simple microscopic
models) is given by nucl-th/0402057. New version extended to include figure
EMMI Rapid Reaction Task Force Meeting on 'Quark Matter in Compact Star'
The recent measurement of two solar mass pulsars has initiated an intense
discussion on its impact on our understanding of the high-density matter in the
cores of neutron stars. A task force meeting was held from October 7-10, 2013
at the Frankfurt Institute for Advanced Studies to address the presence of
quark matter in these massive stars. During this meeting, the recent
oservational astrophysical data and heavy-ion data was reviewed. The
possibility of pure quark stars, hybrid stars and the nature of the QCD phase
transition were discussed and their observational signals delineated.Comment: 31 pages, summary of the EMMI Rapid Reaction Task Force on "Quark
Matter in Compact Stars", October 7-10, 2013, FIAS, Goethe University,
Frankfurt, German
Dynamic migration of rotating neutron stars due to a phase transition instability
Using numerical simulations based on solving the general relativistic
hydrodynamic equations, we study the dynamics of a phase transition in the
dense core of isolated rotating neutron stars, triggered by the back bending
instability reached via angular momentum loss. In particular, we investigate
the dynamics of a migration from an unstable configuration into a stable one,
which leads to a mini-collapse of the neutron star and excites sizeable
pulsations in its bulk until it acquires a new stable equilibrium state. We
consider equations of state with softening at high densities, a simple analytic
one with a mixed hadron-quark phase in an intermediate pressure interval and
pure quark matter at very high densities, and a microphysical one that has a
first-order phase transition, originating from kaon condensation. Although the
marginally stable initial models are rigidly rotating, we observe that during
the collapse (albeit little) differential rotation is created. We analyze the
emission of gravitational radiation, which in some models is amplified by mode
resonance effects, and assess its prospective detectability by interferometric
detectors. We expect that the most favorable conditions for dynamic migration
exist in very young magnetars. We find that the damping of the post-migration
pulsations strongly depends on the character of the equation of state
softening. The damping of pulsations in the models with the microphysical
equation of state is caused by dissipation associated with matter flowing
through the density jump at the edge of the dense core. If at work, this
mechanism dominates over all other types of dissipation, like bulk viscosity in
the exotic-phase core, gravitational radiation damping, or numerical viscosity.Comment: 23 pages, 18 figures, minor modification
Effect of BCS pairing on entrainment in neutron superfluid current in neutron star crust
The relative current density of conduction neutrons in a neutron star
crust beyond the neutron drip threshold can be expected to be related to the
corresponding particle momentum covector by a linear relation of the form
in terms of a physically well defined mobility tensor .
This result is describable as an ``entrainment'' whose effect - wherever the
crust lattice is isotropic - will simply be to change the ordinary neutron mass
m to an effective mass such that in terms of the relevant number
density n of unconfined neutrons we shall have .
In a preceding analysis based on an independent particle treatment using Bloch
boundary conditions to obtain the distribution of energy and associated
group velocity as a function of
wavenumber , it was shown that the mobility tensor would be given by
, where is the
Fermi energy. Using the approach due to Bogoliubov, it is shown here that the
effect of BCS pairing with an energy gap \Delta_F and corresponding
quasiparticle energy function \EE_k=\sqrt{(E_k-\mu)^2+\Delta_F^2}K^{ij}\propto \int d^3 k v_k^i v_k^j \Delta_F^2 /\EE^3_kp_i2|p_i
v_k^i|<\EE_k^2/|E_k-\mu|$ for all modes). It is concluded that the prediction
of a very large effective mass enhancement in the middle layers of the crust
will not be significantly affected by the pairing mechanism.Comment: 30 pages, revised published versio
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Research and Design of a Routing Protocol in Large-Scale Wireless Sensor Networks
无线传感器网络,作为全球未来十大技术之一,集成了传感器技术、嵌入式计算技术、分布式信息处理和自组织网技术,可实时感知、采集、处理、传输网络分布区域内的各种信息数据,在军事国防、生物医疗、环境监测、抢险救灾、防恐反恐、危险区域远程控制等领域具有十分广阔的应用前景。 本文研究分析了无线传感器网络的已有路由协议,并针对大规模的无线传感器网络设计了一种树状路由协议,它根据节点地址信息来形成路由,从而简化了复杂繁冗的路由表查找和维护,节省了不必要的开销,提高了路由效率,实现了快速有效的数据传输。 为支持此路由协议本文提出了一种自适应动态地址分配算——ADAR(AdaptiveDynamicAddre...As one of the ten high technologies in the future, wireless sensor network, which is the integration of micro-sensors, embedded computing, modern network and Ad Hoc technologies, can apperceive, collect, process and transmit various information data within the region. It can be used in military defense, biomedical, environmental monitoring, disaster relief, counter-terrorism, remote control of haz...学位:工学硕士院系专业:信息科学与技术学院通信工程系_通信与信息系统学号:2332007115216
Discutindo a educação ambiental no cotidiano escolar: desenvolvimento de projetos na escola formação inicial e continuada de professores
A presente pesquisa buscou discutir como a Educação Ambiental (EA) vem sendo trabalhada, no Ensino Fundamental e como os docentes desta escola compreendem e vem inserindo a EA no cotidiano escolar., em uma escola estadual do município de Tangará da Serra/MT, Brasil. Para tanto, realizou-se entrevistas com os professores que fazem parte de um projeto interdisciplinar de EA na escola pesquisada. Verificou-se que o projeto da escola não vem conseguindo alcançar os objetivos propostos por: desconhecimento do mesmo, pelos professores; formação deficiente dos professores, não entendimento da EA como processo de ensino-aprendizagem, falta de recursos didáticos, planejamento inadequado das atividades. A partir dessa constatação, procurou-se debater a impossibilidade de tratar do tema fora do trabalho interdisciplinar, bem como, e principalmente, a importância de um estudo mais aprofundado de EA, vinculando teoria e prática, tanto na formação docente, como em projetos escolares, a fim de fugir do tradicional vínculo “EA e ecologia, lixo e horta”.Facultad de Humanidades y Ciencias de la Educació
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