1,961 research outputs found
Double-core evolution and the formation of neutron-star binaries with compact companions
We present the results of a systematic exploration of an alternative
evolutionary scenario to form double neutron-star binaries, first proposed by
Brown (1995), which does not involve a neutron star passing through a common
envelope. In this scenario, the initial binary components have very similar
masses, and both components have left the main sequence before they evolve into
contact; preferably the primary has already developed a CO core. We have
performed population synthesis simulations to study the formation of double
neutron star binaries via this channel and to predict the orbital properties
and system velocities of such systems. We obtain a merger rate for DNSs in this
channel in the range of 0.1 - 12/Myr. These rates are still subject to
substantial uncertainties such as the modelling of the contact phase.Comment: MNRAS, accepte
Seismic strengthening of beam-column joints with multidirectional CFRP laminates
An experimental program was carried out to analyse the potentialities of a technique based on the use of multidirectional CFRP laminates (MDL-CFRP) for the seismic repair and strengthening of reinforced concrete (RC) beam-column joints. This experimental program comprises cyclic tests on three full-scale RC joints, representative of interior beam-column connections in buildings. The joints were initially submitted to a cyclic test inducing a
damage pattern representative of a seismic event. Subsequently, they were repaired and
strengthened with MDL-CFRP. The strengthened joints were then tested for the same loading
history of the original ones up to their failure. The adopted strengthening technique uses the MDL-CFRP that are simultaneously glued and anchored to the concrete surfaces. This technique is called Mechanically Fastened and Externally Bonded Reinforcement (MF-EBR).
In the present study, the effectiveness of two different strengthening configurations was investigated. The tests are described and the main results are presented and analyzed
Oral Contraceptive Use and Clinical Outcomes in Patients with Multiple Sclerosis
Experimental and clinical data suggest a role of sex steroids in the pathogenesis of multiple sclerosis (MS). Scant information is available about the potential effect of oral contraceptive (OC) use on the prognosis of the disease. We aimed to evaluate this. The study population consisted of 132 women with relapsing-remitting MS before receiving disease modifying treatment and a mean disease duration 6.2 (SD 5.1) years. Three groups of patients were distinguished according to their OC behavior: [1] never-users, patients who never used OC [2] past-users, patients who stopped OC use before disease onset, and [3] after-users, those who used these drugs after disease onset. Multiple linear and logistic regression models were used to analyze the association between oral contraceptive use and annualized relapse rates, disability accumulation and severity of the disease. After-user patients had lower Expanded Disability Status Scale (EDSS) and Multiple Sclerosis Severity Score (MSSS) values than never users (p<0.001 and p=0.002, respectively) and past users (p=0.010 and p=0.002, respectively). These patients were also more likely to have a benign disease course (MSSS<2.5) than never and past users together (OR: 4.52, 95%CI: 2.13-9.56, p<0.001). This effect remained significant after adjustment for confounders, including smoking and childbirths (OR: 2.97, 95%CI: 1.24, 6.54, p=0.011 and for MSSS β: -1.04; 95% C.I. -1.78, -0.30, p=0.006). These results suggest that OC use in women with relapsing-remitting MS is possible associated with a milder disabling disease course
Development of an integrated heat pipe-thermal storage system for a solar receiver
The Organic Rankine Cycle (ORC) Solar Dynamic Power System (SDPS) is one of the candidates for Space Station prime power application. In the low Earth orbit of the Space Station approximately 34 minutes of the 94-minute orbital period is spent in eclipse with no solar energy input to the power system. For this period the SDPS will use thermal energy storage (TES) material to provide a constant power output. An integrated heat-pipe thermal storage receiver system is being developed as part of the ORC-SDPS solar receiver. This system incorporates potassium heat pipe elements to absorb and transfer the solar energy within the receiver cavity. The heat pipes contain the TES canisters within the potassium vapor space with the toluene heater tube used as the condenser region of the heat pipe. During the insolation period of the Earth orbit, solar energy is delivered to the heat pipe in the ORC-SDPS receiver cavity. The heat pipe transforms the non-uniform solar flux incident in the heat pipe surface within the receiver cavity to an essentially uniform flux at the potassium vapor condensation interface in the heat pipe. During solar insolation, part of the thermal energy is delivered to the heater tube and the balance is stored in the TES units. During the eclipse period of the orbit, the balance stored in the TES units is transferred by the potassium vapor to the toluene heater tube
Probing the two-scale-factor universality hypothesis by exact rotation symmetry-breaking mechanism
We probe the two-scale factor universality hypothesis by evaluating, firstly
explicitly and analytically at the one-loop order, the loop quantum corrections
to the amplitude ratios for O() scalar field theories with
rotation symmetry-breaking in three distinct and independent methods in which
the rotation symmetry-breaking mechanism is treated exactly. We show that the
rotation symmetry-breaking amplitude ratios turn out to be identical in the
three methods and equal to their respective rotation symmetry-breaking ones,
although the amplitudes themselves, in general, depend on the method employed
and on the rotation symmetry-breaking parameter. At the end, we show that all
these results can be generalized, through an inductive process based on a
general theorem emerging from the exact calculation, to any loop level and
physically interpreted based on symmetry ideas.Comment: 17 pages, 3 figure
Fabrication and Testing of Mo-Re Heat Pipes Embedded in Carbon/Carbon
Refractory-composite/heat-pipe-cooled wing an tail leading edges are being considered for use on hypersonic vehicles to limit maximum temperatures to values below material reuse limits and to eliminate the need to actively cool the leading edges. The development of a refractory-composite/heat-pipe-cooled leading edge has evolved from the design stage to the fabrication and testing of heat pipes embedded in carbon/carbon (C/C). A three-foot-long, molybdenum-rhenium heat pipe with a lithium working fluid was fabricated and tested at an operating temperature of 2460 F to verify the individual heat-pipe design. Following the fabrication of this heat pipe, three additional heat pipes were fabricated and embedded in C/C. The C/C heat-pipe test article was successfully tested using quartz lamps in a vacuum chamber in both a horizontal and vertical orientation. Start up and steady state data are presented for the C/C heat-pipe test article. Radiography and eddy current evaluations were performed on the test article
Start Up of a Nb-1%Zr Potassium Heat Pipe From the Frozen State
The start up of a liquid metal heat pipe from the frozen state was evaluated experimentally with a Nb-1%Zr heat pipe with potassium as the working fluid. The heat pipe was fabricated and tested at Los Alamos National Laboratory. RF induction heating was used to heat 13 cm of the 1-m-long heat pipe. The heat pipe and test conditions are well characterized so that the test data may be used for comparison with numerical analyses. An attempt was made during steady state tests to calibrate the heat input so that the heat input would be known during the transient cases. The heat pipe was heated to 675 C with a throughput of 600 W and an input heat flux of 6 W/cm(exp 2). Steady state tests, start up from the frozen state, and transient variations from steady state were performed
Viabilidade econômica do manejo de açaizais no estuário amazônico: estudo de caso na região do Rio Tauerá-açu, Abaetetuba - estado do Pará.
O objetivo deste estudo foi avaliar comparativamente o desempenho socioeconômico e a viabilidade econômica de sistemas produtivos de açaí manejado adotado pelos produtores e recomendado pela pesquisa agropecuária, em áreas de várzeas do estuário do rio Amazonas, no Estado do Pará. A coleta de dados para a análise do sistema de produção ocorreu por meio de entrevistas individuais com produtores e técnicos e pela realização de painéis técnicos reunindo produtores com experiência no desenvolvimento da atividade de manejo de açaizais. Foram estimados indicadores de rentabilidade e de viabilidade econômico-financeira para determinação do desempenho dos sistemas e realizadas análises de sensibilidade a variações de preços. Os resultados mostraram que tanto o sistema adotado pelo produtor quanto o sistema recomendado pela pesquisa apresentaram eficiência e viabilidade econômica, nas condições de produção e de mercado predominantes, com melhor desempenho e estabilidade para o sistema recomendado. A atividade de colheita é a etapa que representa maior custo no processo produtivo
Seismic retrofit of RC beam-column joints using the MF-EBR strengthening technique
The strengthening technique based on the application of multi-directional
laminates of CFRP (MDL-CFRP) simultaneously glued and anchored to the surface
of the elements to be strengthened has been recently proposed. This technique was
designated Mechanically Fastened and Externally Bonded Reinforcement (MF-EBR)
and combines the fasteners from the MF-FRP technique with the externally glued
properties from the EBR. With the aim of assessing the potentialities of this technique
for seismic retrofitting, three interior RC beam-column joints were strengthened
according to the MF-EBR technique and tested. This work presents the entire test
program executed, including test configuration, results and corresponding analysis
- …