9,976 research outputs found
Optimal Trajectories for Near-Earth-Objects Using Solar Electric Propulsion (SEP) and Gravity Assisted Maneuver
The future interplanetary missions will probably use the conventional chemical rockets to leave the sphere of influence of the Earth, and solar electric propulsion (SEP) to accomplish the other maneuvers of the mission. In this work the optimization of interplanetary missions using solar electric propulsion and Gravity Assisted Maneuver to reduce the costs of the mission, is considered. The high specific impulse of electric propulsion makes a Gravity Assisted Maneuver 1 year after departure convenient. Missions for several Near Earth Asteroids will be considered. The analysis suggests criteria for the definition of initial solutions demanded for the process of optimization of trajectories. Trajectories for the asteroid 2002TC70 are analyzed. Direct trajectories, trajectories with 1 gravity assisted from the Earth and with 2 gravity assisted from the Earth and either Mars are present. An indirect optimization method will be used in the simulations
On a novel approach for optimizing composite materials panel using surrogate models
This paper describes an optimization procedure to design thermoplastic composite panels under axial compressive load conditions. Minimum weight is the goal. The panel design is subject to buckling constraints. The presence of the bending-twisting coupling and of particular boundary conditions does not allow an analytical solution for the critical buckling load. Surrogate models are used to approximate the buckling response of the plate in a fast and reliable way. Therefore, two surrogate models are compared to study their effectiveness in composite optimization. The first one is a linear approximation based on the buckling constitutive equation. The second consists in the application of the Kriging surrogate. Constraints given from practical blending rules are also introduced in the optimization. Discrete values of ply thicknesses is a requirement. An ad-hoc discrete optimization strategy is developed, which enables to handle discrete variables
Spectra of ultrabroadband squeezed pulses and the finite-time Unruh-Davies effect
We study spectral properties of quantum radiation of ultimately short
duration. In particular, we introduce a continuous multimode squeezing operator
for the description of subcycle pulses of entangled photons generated by a
coherent-field driving in a thin nonlinear crystal with second order
susceptibility. We find the ultrabroadband spectra of the emitted quantum
radiation perturbatively in the strength of the driving field. These spectra
can be related to the spectra expected in an Unruh-Davies experiment with a
finite time of acceleration. In the time domain, we describe the corresponding
behavior of the normally ordered electric field variance.Comment: 11 pages, 5 figure
Universal rates for reactive ultracold polar molecules in reduced dimensions
Analytic expressions describe universal elastic and reactive rates of
quasi-two-dimensional and quasi-one-dimensional collisions of highly reactive
ultracold molecules interacting by a van der Waals potential. Exact and
approximate calculations for the example species of KRb show that stability and
evaporative cooling can be realized for spin-polarized fermions at moderate
dipole and trapping strength, whereas bosons or unlike fermions require
significantly higher dipole or trapping strengths.Comment: 4 pages, 3 figure
Recommended from our members
Microconfined flow behavior of red blood cells by image analysis techniques
This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.Red blood cells (RBCs) perform essential functions in human body, such as gas exchange between
blood and tissues, thanks to their ability to deform and flow in the microvascular network. The high RBC
deformability is mainly due to the viscoelastic properties of the cell membrane. Since an impaired RBC
deformability could be found in some diseases, such as malaria, sickle cell anemia, diabetes and hereditary
disorders, there is the need to provide further insight into measurement of RBC deformability in a
physiologically-relevant flow field. Here, we report on an imaging-based in vitro systematic microfluidic
investigation of RBCs flowing either in microcapillaries or in a microcirculation-mimicking device
containing a network of microchannels of diameter comparable to cell size. RBC membrane shear elastic
modulus and surface viscosity have been investigated by using diverging channels, while RBC time recovery
constant have been measured in start-up experiments. Moreover, RBC volume and surface area have been
measured in microcapillary flow. The comprehension of the single cell behavior led to the analysis of the
RBC flow-induced clustering. Overall, our results provide a novel technique to estimate RBC deformability,
that can be used for the analysis of pathological RBCs, for which reliable quantitative methods are still
lacking
Pseudo-fermionization of 1-D bosons in optical lattices
We present a model that generalizes the Bose-Fermi mapping for strongly
correlated 1D bosons in an optical lattice, to cases in which the average
number of atoms per site is larger than one. This model gives an accurate
account of equilibrium properties of such systems, in parameter regimes
relevant to current experiments. The application of this model to
non-equilibrium phenomena is explored by a study of the dynamics of an atom
cloud subject to a sudden displacement of the confining potential. Good
agreement is found with results of recent experiments. The simplicity and
intuitive appeal of this model make it attractive as a general tool for
understanding bosonic systems in the strongly correlated regime.Comment: 5 pages, 4 figure
Extreme-Point-based Heuristics for the Three-Dimensional Bin Packing problem
One of the main issues in addressing three-dimensional packing problems is finding an efficient and accurate definition of the points at which to place the items inside the bins, because the performance of exact and heuristic solution methods is actually strongly influenced by the choice of a placement rule. We introduce the extreme point concept and present a new extreme point-based rule for packing items inside a three-dimensional container. The extreme point rule is independent from the particular packing problem addressed and can handle additional constraints, such as fixing the position of the items. The new extreme point rule is also used to derive new constructive heuristics for the three-dimensional bin-packing problem. Extensive computational results show the effectiveness of the new heuristics compared to state-of-the-art results. Moreover, the same heuristics, when applied to the two-dimensional bin-packing problem, outperform those specifically designed for the proble
Chemical constituents, toxicity and antimicrobial activities of the essential oil of the leaves of Tectona grandis
The leaves of Tectona grandis (Verbanaceae) was subjected to hydrodistillation in order to obtain the essential oil from the plant. The pale yellow essential oil gave a percentage yield of 0.184%. Relative percentages of individual component were analyzed by GC/GC-MS. A total of fifty-four (54) constituents were identified representing 86.5% of the total essential oil fraction. Oxygenated monoterpenes, sesquiterpene hydrocarbons, oxygenated sesquiterpenes, apocarotenoids, phenylpropanoids and non-terpene derivatives were the various classes of compounds identified. The LC50 value from the brine shrimp toxicity assay was 183.29µg/ml. The oil extract was also subjected to antibacterial assay and it showed significant activities against all the clinical test organisms used except Pseudomonas aeruginos
- …