24,638 research outputs found
Searching for a preferred direction with Union2.1 data
A cosmological preferred direction was reported from the type Ia supernovae
(SNe Ia) data in recent years. We use the Union2.1 data to give a simple
classification of such studies for the first time. Because the maximum
anisotropic direction is independent of isotropic dark energy models, we adopt
two cosmological models (CDM, CDM) for the hemisphere comparison
analysis and CDM model for dipole fit approach. In hemisphere
comparison method, the matter density and the equation of state of dark energy
are adopted as the diagnostic qualities in the CDM model and CDM
model, respectively. In dipole fit approach, we fit the fluctuation of distance
modulus. We find that there is a null signal for the hemisphere comparison
method, while a preferred direction () for the dipole fit method. This result indicates
that the dipole fit is more sensitive than the hemisphere comparison method.Comment: 8 pages, 2 figures, accepted for publication in MNRA
Pressure-Temperature Phase Diagram of Multiferroic
The pressure-temperature phase diagram of multiferroic is
investigated for hydrostatic pressures up to 2 GPa. The stability range of the
ferroelectric phase associated with the incommensurate helical spin order is
reduced by pressure and ferroelectricity is completely suppressed at the
critical pressure of 1.64 GPa at 6.2 K. Thermal expansion measurements at
ambient pressure show strong step-like anomalies of the lattice parameters
associated with the lock-in transition into the commensurate paraelectric
phase. The expansion anomalies are highly anisotropic, the related volume
change is consistent with the high-pressure phase diagram
Crescimento e nutrição mineral de mudas de mangostão (Garcinia mangostana L.) micorrizadas ou não, em substrato com ou sem matéria orgânica.
bitstream/item/32688/1/CPATU-BP136.pd
Plasma-Like Negative Capacitance in Nano-Colloids
A negative capacitance has been observed in a nano-colloid between 0.1 and
10^-5 Hz. The response is linear over a broad range of conditions. The
low-omega dispersions of both the resistance and capacitance are consistent
with the free-carrier plasma model, while the transient behavior demonstrates
an unusual energy storage mechanism. A collective excitation, therefore, is
suggested.Comment: 3 pages, 3 figure
Neutron scattering study of novel magnetic order in Na0.5CoO2
We report polarized and unpolarized neutron scattering measurements of the
magnetic order in single crystals of Na0.5CoO2. Our data indicate that below
T_N=88 K the spins form a novel antiferromagnetic pattern within the CoO2
planes, consisting of alternating rows of ordered and non-ordered Co ions. The
domains of magnetic order are closely coupled to the domains of Na ion order,
consistent with such a two-fold symmetric spin arrangement. Magnetoresistance
and anisotropic susceptibility measurements further support this model for the
electronic ground state.Comment: 4 pages, 4 figure
Linearization and Decomposition Methods for Large Scale Stochastic Inventory Routing Problem with Service Level Constraints
A stochastic inventory routing problem (SIRP) is typically the combination of stochastic inventory control problems and NP-hard vehicle routing problems, for a depot to determine delivery volumes to its customers in each period, and vehicle routes to distribute the delivery volumes. This paper aims to solve a large scale multi-period SIRP with split delivery (SIRPSD) where a customer’s delivery in each period can be split and satisfied by multiple vehicles if necessary. The objective of the problem is to minimize the total inventory and transportation cost while some constraints are given to satisfy other criteria, such as the service level to limit the stockout probability at each customer and the service level to limit the overfilling probability of the warehouse of each customer. In order to tackle the SIRPSD with notorious computational complexity, we propose for it an approximate model, which significantly reduces the number of decision variables compared to its corresponding exact model. We develop a hybrid approach that combines the linearization of nonlinear constraints, the decomposition of the model into sub-models with Lagrangian relaxation, and a partial linearization approach for a sub model. A near optimal solution of the model can be found by the approach, and then be used to construct a near optimal solution of the SIRPSD. Numerical examples show that, for an instance of the problem with 200 customers and 5 periods that contains about 400 thousands decision variables where half of them are integer, our approach can obtain high quality near optimal solutions with a reasonable computational time on an ordinary PC
Strong spin-lattice coupling in multiferroic HoMnO: Thermal expansion anomalies and pressure effect
Evidence for a strong spin-lattice coupling in multiferroic HoMnO_3 is
derived from thermal expansion measurements along a- and c-axis. The
magnetoelastic effect results in sizable anomalies of the thermal expansivities
at the antiferromagnetic (T_N) and the spin rotation (T_{SR}) transition
temperatures as well as in a negative c-axis expansivity below room
temperature. The coupling between magnetic orders and dielectric properties
below T_N is explained by the lattice strain induced by the magnetoelastic
effect. At T_{SR} various physical quantities show discontinuities that are
thermodynamically consistent with a first order phase transition
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