5,940 research outputs found
On Matrix Product States for Periodic Boundary Conditions
The possibility of a matrix product representation for eigenstates with
energy and momentum zero of a general m-state quantum spin Hamiltonian with
nearest neighbour interaction and periodic boundary condition is considered.
The quadratic algebra used for this representation is generated by 2m operators
which fulfil m^2 quadratic relations and is endowed with a trace. It is shown
that {\em not} every eigenstate with energy and momentum zero can be written as
matrix product state. An explicit counter-example is given. This is in contrast
to the case of open boundary conditions where every zero energy eigenstate can
be written as a matrix product state using a Fock-like representation of the
same quadratic algebra.Comment: 7 pages, late
Role of the total isospin 3/2 component in three-nucleon reactions
We discuss the role of the three-nucleon isospin T=3/2 amplitude in elastic
neutron-deuteron scattering and in the deuteron breakup reaction. The
contribution of this amplitude originates from charge-independence breaking of
the nucleon-nucleon potential and is driven by the difference between
neutron-neutron (proton-proton) and neutron-proton forces. We study the
magnitude of that contribution to the elastic scattering and breakup
observables, taking the locally regularized chiral N4LO nucleon-nucleon
potential supplemented by the chiral N2LO three-nucleon force. For comparison
we employ also the Av18 nucleon-nucleon potential combined with the Urbana IX
three-nucleon force. We find that the isospin T=3/2 component is important for
the breakup reaction and the proper treatment of charge-independence breaking
in this case requires the inclusion of the 1S0 state with isospin T=3/2. For
neutron-deuteron elastic scattering the T=3/2 contributions are insignificant
and charge-independence breaking can be accounted for by using the effective
t-matrix generated with the so-called "2/3-1/3" rule.Comment: 24 pages, 8 figures, 3 Table
Investigating the genetic and environmental aetiologies of non-suicidal and suicidal self-harm: a twin study
BACKGROUND: Self-harm is a major health concern, not only as a signal of distress but also as a strong predictor of later suicide. Self-harm can be further refined into suicidal self-harm (SSH, i.e. suicide attempt) and non-suicidal self-harm (NSSH). Understanding the aetiologies of NSSH and SSH can help inform suicide prevention strategies. Using a twin design, we investigated the phenotypic and aetiological relationships between NSSH and SSH, and their aetiological overlap with mental health problems. METHODS: We analysed data from the Twins Early Development Study using structural equation modelling. At age 21 years, 9063 twins (62.4% female) answered questions related to self-harm. At age 16 years, 19 self- or parent-reported mental health measures were administered, including measures of internalising and externalising problems, psychotic-like experiences and substance abuse. RESULTS: Prevalences for NSSH and SSH were 21.9% and 10.5%, respectively. Additive genetic factors explained half of the variance in NSSH (55%) and SSH (50%), with the rest explained by non-shared environmental factors. Phenotypically, NSSH and SSH were strongly correlated (r = 0.87) with their correlation explained by genetic (57%) and non-shared environmental (43%) factors. We found no evidence that NSSH and SSH differed in their phenotypic and aetiological relationships with mental health measures. CONCLUSION: Our findings suggest no aetiological difference between NSSH and SSH. NSSH and SSH should be regarded as two different ends of a continuum, rather than as two distinct categories
The Study of Shocks in Three-States Driven-Diffusive Systems: A Matrix Product Approach
We study the shock structures in three-states one-dimensional
driven-diffusive systems with nearest neighbors interactions using a matrix
product formalism. We consider the cases in which the stationary probability
distribution function of the system can be written in terms of superposition of
product shock measures. We show that only three families of three-states
systems have this property. In each case the shock performs a random walk
provided that some constraints are fulfilled. We calculate the diffusion
coefficient and drift velocity of shock for each family.Comment: 15 pages, Accepted for publication in Journal of Statistical
Mechanics: Theory and Experiment (JSTAT
Drops for stuff: An analysis of reshipping mule scams
Credit card fraud has seen rampant increase in the past years, as customers use credit cards and similar financial instruments frequently. Both online and brick-and-mortar outfits repeatedly fall victim to cybercriminals who siphon off credit card information in bulk. Despite the many and creative ways that attackers use to steal and trade credit card information, the stolen information can rarely be used to withdraw money directly, due to protection mechanisms such as PINs and cash advance limits. As such, cybercriminals have had to devise more advanced monetization schemes towork around the current restrictions. One monetization scheme that has been steadily gaining traction are reshipping scams. In such scams, cybercriminals purchase high-value or highly-demanded products from online merchants using stolen payment instruments, and then ship the items to a credulous citizen. This person, who has been recruited by the scammer under the guise of "work-from-home" opportunities, then forwards the received products to the cybercriminals, most of whom are located overseas. Once the goods reach the cybercriminals, they are then resold on the black market for an illicit profit. Due to the intricacies of this kind of scam, it is exceedingly difficult to trace, stop, and return shipments, which is why reshipping scams have become a common means for miscreants to turn stolen credit cards into cash. In this paper, we report on the first large-scale analysis of reshipping scams, based on information that we obtained from multiple reshipping scam websites. We provide insights into the underground economy behind reshipping scams, such as the relationships among the various actors involved, the market size of this kind of scam, and the associated operational churn. We find that there exist prolific reshipping scam operations, with one having shipped nearly 6,000 packages in just 9 months of operation, exceeding 7.3 million US dollars in yearly revenue, contributing to an overall reshipping scam revenue of an estimated 1.8 billion US dollars per year. Finally, we propose possible approaches to intervene and disrupt reshipping scam services
Construction of a matrix product stationary state from solutions of finite size system
Stationary states of stochastic models, which have states per site, in
matrix product form are considered. First we give a necessary condition for the
existence of a finite -dimensional matrix product state for any .
Second, we give a method to construct the matrices from the stationary states
of small size system when the above condition and are satisfied.
Third, the method by which one can check that the obtained matrices are valid
for any system size is presented for the case where is satisfied. The
application of our methods is explained using three examples: the asymmetric
exclusion process, a model studied in [F. H. Jafarpour: J. Phys. A: Math. Gen.
36 (2003) 7497] and a hybrid of both of the models.Comment: 22 pages, no figure. Major changes: sec.3 was shortened; the list of
references were changed. This is the final version, which will appear in
J.Phys.
Ergodicity breaking in one-dimensional reaction-diffusion systems
We investigate one-dimensional driven diffusive systems where particles may
also be created and annihilated in the bulk with sufficiently small rate. In an
open geometry, i.e., coupled to particle reservoirs at the two ends, these
systems can exhibit ergodicity breaking in the thermodynamic limit. The
triggering mechanism is the random motion of a shock in an effective potential.
Based on this physical picture we provide a simple condition for the existence
of a non-ergodic phase in the phase diagram of such systems. In the
thermodynamic limit this phase exhibits two or more stationary states. However,
for finite systems transitions between these states are possible. It is shown
that the mean lifetime of such a metastable state is exponentially large in
system-size. As an example the ASEP with the A0A--AAA reaction kinetics is
analyzed in detail. We present a detailed discussion of the phase diagram of
this particular model which indeed exhibits a phase with broken ergodicity. We
measure the lifetime of the metastable states with a Monte Carlo simulation in
order to confirm our analytical findings.Comment: 25 pages, 14 figures; minor alterations, typos correcte
Positive and Negative Emotions Predict Weight Loss Intentions and Behaviors beyond Theory of Planned Behavior Constructs
Acknowledgements: This study was funded by the ScienceCampus Tuebingen (TP7.1) awarded to Devin G. Ray and Kai Sassenberg.Peer reviewedPostprin
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