6,314 research outputs found
Remarks on Characterizations of Malinowska and Szynal
The problem of characterizing a distribution is an important problem which has recently attracted the attention of many researchers. Thus, various characterizations have been established in many different directions. An investigator will be vitally interested to know if their model fits the requirements of a particular distribution. To this end, one will depend on the characterizations of this distribution which provide conditions under which the underlying distribution is indeed that particular distribution. In this work, several characterizations of Malinowska and Szynal (2008) for certain general classes of distributions are revisited and simpler proofs of them are presented. These characterizations are not based on conditional expectation of the kth lower record values (as in Malinowska and Szynal), they are based on: (i) simple truncated moments of the random variable, (ii) hazard function
A new 3D-beam finite element including non-uniform torsion with the secondary torsion moment deformation effect
In this paper, a new 3D Timoshenko linear-elastic beam finite element including warping torsion will be presented which is suitable for analysis of spatial structures consisting of constant open and hollow structural section (HSS) beams. The analogy between the 2ndorder beam theory (with axial tension) and torsion (including warping) was used for the formulation of the equations for non-uniform torsion. The secondary torsional moment deformation effect and the shear force effect are included into the local beam finite element stiffness matrix. The warping part of the first derivative of the twist angle was considered as an additional degree of freedom at the finite element nodes. This degree of freedom represents a part of the twist angle curvature caused by the bimoment. Results of the numerical experiments are discussed, compared and evaluated. The importance of the inclusion of warping in stress-deformation analyses of closed-section beams is demostrated
Attention explores space periodically at the theta frequency
Voluntary attention is at the core of a wide variety of cognitive functions. Attention can be oriented to and sustained at a location or reoriented in space to allow processing at other locations—critical in an ever-changing environment. Numerous studies have investigated attentional orienting in time and space, but little is known about the spatiotemporal dynamics of attentional reorienting. Here we explicitly manipulated attentional reorienting using a cuing procedure in a two- alternative forced-choice orientation-discrimination task. We interrogated attentional distribution by flashing two probe stimuli with various delays between the precue and target stimuli. Then we used the probabilities that both probes and neither probe were correctly reported to solve a second-degree equation, which estimates the report probability at each probe location. We demonstrated that attention reorients periodically at ~4 Hz (theta) between the two stimulus locations. We further characterized the processing dynamics at each stimulus location, and demonstrated that attention samples each location periodically at ;11 Hz (alpha). Finally, simulations support our findings and show that this method is sufficiently powered, making it a valuable tool for studying the spatiotemporal dynamics of attention
Lower bounds for polynomials using geometric programming
We make use of a result of Hurwitz and Reznick, and a consequence of this
result due to Fidalgo and Kovacec, to determine a new sufficient condition for
a polynomial of even degree to be a sum of
squares. This result generalizes a result of Lasserre and a result of Fidalgo
and Kovacec, and it also generalizes the improvements of these results given in
[6]. We apply this result to obtain a new lower bound for , and we
explain how can be computed using geometric programming. The lower
bound is generally not as good as the lower bound introduced
by Lasserre and Parrilo and Sturmfels, which is computed using semidefinite
programming, but a run time comparison shows that, in practice, the computation
of is much faster. The computation is simplest when the highest degree
term of has the form , , . The
lower bounds for established in [6] are obtained by evaluating the
objective function of the geometric program at the appropriate feasible points
Communication through coherent control of quantum channels
A completely depolarising quantum channel always outputs a fully mixed state
and thus cannot transmit any information. In a recent Letter [D. Ebler et al.,
Phys. Rev. Lett. 120, 120502 (2018)], it was however shown that if a quantum
state passes through two such channels in a quantum superposition of different
orders - a setup known as the "quantum switch" - then information can
nevertheless be transmitted through the channels. Here, we show that a similar
effect can be obtained when one coherently controls between sending a target
system through one of two identical depolarising channels. Whereas it is
tempting to attribute this effect in the quantum switch to the indefinite
causal order between the channels, causal indefiniteness plays no role in this
new scenario. This raises questions about its role in the corresponding effect
in the quantum switch. We study this new scenario in detail and we see that,
when quantum channels are controlled coherently, information about their
specific implementation is accessible in the output state of the joint
control-target system. This allows two different implementations of what is
usually considered to be the same channel to therefore be differentiated. More
generally, we find that to completely describe the action of a coherently
controlled quantum channel, one needs to specify not only a description of the
channel (e.g., in terms of Kraus operators), but an additional "transformation
matrix" depending on its implementation.Comment: 14 pages, 2 figure
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