18,346 research outputs found
Energy-Efficient Resource Allocation in Wireless Networks with Quality-of-Service Constraints
A game-theoretic model is proposed to study the cross-layer problem of joint
power and rate control with quality of service (QoS) constraints in
multiple-access networks. In the proposed game, each user seeks to choose its
transmit power and rate in a distributed manner in order to maximize its own
utility while satisfying its QoS requirements. The user's QoS constraints are
specified in terms of the average source rate and an upper bound on the average
delay where the delay includes both transmission and queuing delays. The
utility function considered here measures energy efficiency and is particularly
suitable for wireless networks with energy constraints. The Nash equilibrium
solution for the proposed non-cooperative game is derived and a closed-form
expression for the utility achieved at equilibrium is obtained. It is shown
that the QoS requirements of a user translate into a "size" for the user which
is an indication of the amount of network resources consumed by the user. Using
this competitive multiuser framework, the tradeoffs among throughput, delay,
network capacity and energy efficiency are studied. In addition, analytical
expressions are given for users' delay profiles and the delay performance of
the users at Nash equilibrium is quantified.Comment: Accpeted for publication in the IEEE Transactions on Communication
Lexipol\u27s Fight Against Police Reform
We are in the midst of a critically important moment in police reform. National and local attention is fixed on how to reduce the number of people killed and injured by the police. One approach—which has been recognized for decades to reduce police killings—is to limit police power to use force.
This Article is the first to uncover how an often-overlooked private company, Lexipol LLC, has become one of the most powerful voices pushing against reform of use-of-force standards. Founded in 2003, Lexipol now writes police policies and trainings for over one-fifth of American law enforcement agencies. As this Article documents, Lexipol has refused to incorporate common reform proposals into the policies it writes for its subscribers, including a use-of-force matrix, policies requiring de-escalation, or bright-line rules prohibiting chokeholds and shooting into cars. Lexipol has also taken an active advocacy role in opposition to proposed reforms of police use-of-force standards, pushing, instead, for departments to hew closely to Graham v. Connor’s “objectively reasonable” standard. Finally, when use-of-force reforms have been enacted, Lexipol has attempted to minimize their impact.
Local governments, police departments, and insurers have long viewed Lexipol as a critically important partner in keeping policies lawful and up to date. This Article makes clear that they should take a closer look. Lexipol’s aggressive efforts to retain wide officer discretion to use force may ultimately expose officers and agencies to liability instead of shielding them from it. It is time for advocacy groups seeking policing improvements to train their sights on Lexipol. Unless and until Lexipol changes its approach, the company should be viewed as a barrier to reform. * Professors of Law, UCLA School of Law. For thoughtful comments on prior drafts, we than
Generalized Supersymmetric Perturbation Theory
Using the basic ingredient of supersymmetry, we develop a simple alternative
approach to perturbation theory in one-dimensional non-relativistic quantum
mechanics. The formulae for the energy shifts and wave functions do not involve
tedious calculations which appear in the available perturbation theories. The
model applicable in the same form to both the ground state and excited bound
states, unlike the recently introduced supersymmetric perturbation technique
which, together with other approaches based on logarithmic perturbation theory,
are involved within the more general framework of the present formalism.Comment: 13 pages article in LaTEX (uses standard article.sty). No Figures.
Sent to Ann. Physics (2004
Modeling and analysis of an auto-adjustable stroke end cushioning device for hydraulic cylinders
Temporal Correlations of Local Network Losses
We introduce a continuum model describing data losses in a single node of a
packet-switched network (like the Internet) which preserves the discrete nature
of the data loss process. {\em By construction}, the model has critical
behavior with a sharp transition from exponentially small to finite losses with
increasing data arrival rate. We show that such a model exhibits strong
fluctuations in the loss rate at the critical point and non-Markovian power-law
correlations in time, in spite of the Markovian character of the data arrival
process. The continuum model allows for rather general incoming data packet
distributions and can be naturally generalized to consider the buffer server
idleness statistics
On Collisionless Electron-Ion Temperature Equilibration in the Fast Solar Wind
We explore a mechanism, entirely new to the fast solar wind, of electron
heating by lower hybrid waves to explain the shift to higher charge states
observed in various elements in the fast wind at 1 A.U. relative to the
original coronal hole plasma. This process is a variation on that previously
discussed for two temperature accretion flows by Begelman & Chiueh. Lower
hybrid waves are generated by gyrating minor ions (mainly alpha-particles) and
become significant once strong ion cyclotron heating sets in beyond 1.5 R_sun.
In this way the model avoids conflict with SUMER electron temperature
diagnostic measurements between 1 and 1.5 R_sun. The principal requirement for
such a process to work is the existence of density gradients in the fast solar
wind, with scale length of similar order to the proton inertial length. Similar
size structures have previously been inferred by other authors from radio
scintillation observations and considerations of ion cyclotron wave generation
by global resonant MHD waves.Comment: 32 pages including 11 figures, 4 tables, accepted by Ap
Random Walks in Local Dynamics of Network Losses
We suggest a model for data losses in a single node of a packet-switched
network (like the Internet) which reduces to one-dimensional discrete random
walks with unusual boundary conditions. The model shows critical behavior with
an abrupt transition from exponentially small to finite losses as the data
arrival rate increases. The critical point is characterized by strong
fluctuations of the loss rate. Although we consider the packet arrival being a
Markovian process, the loss rate exhibits non-Markovian power-law correlations
in time at the critical point.Comment: 4 pages, 2 figure
Open ventral hernia repair with a composite ventral patch : final results of a multicenter prospective study
Background: This study assessed clinical outcomes, including safety and recurrence, from the two-year follow-up of patients who underwent open ventral primary hernia repair with the use of the Parietex (TM) Composite Ventral Patch (PCO-VP).
Methods: A prospective single-arm, multicenter study of 126 patients undergoing open ventral hernia repair for umbilical and epigastric hernias with the PCO-VP was performed.
Results: One hundred twenty-six subjects (110 with umbilical hernia and 16 with epigastric hernia) with a mean hernia diameter of 1.8cm (0.4-4.0) were treated with PCO-VP. One hundred subjects completed the two-year study. Cumulative hernia recurrence was 3.0% (3/101; 95%CI: 0.0-6.3%) within 24months. Median Numeric Rating Scale pain scores improved from 2 [0-10] at baseline to 0 [0-3] at 1 month (P<0.001) and remained low at 24months 0 [0-6] (P<0.001). 99% (102/103) of the patients were satisfied with their repair at 24months postoperative.
Conclusions: The use of PCO-VP to repair primary umbilical and epigastric defects yielded a low recurrence rate, low postoperative and chronic pain, and high satisfaction ratings, confirming that PCO-VP is effective for small ventral hernia repair in the two-year term after implantation.
Trial registration: The study was registered publically at clinicaltrials.gov (NCT01848184 registered May 7, 2013)
Solutions of multigravity theories and discretized brane worlds
We determine solutions to 5D Einstein gravity with a discrete fifth
dimension. The properties of the solutions depend on the discretization scheme
we use and some of them have no continuum counterpart. In particular, we find
that the neglect of the lapse field (along the discretized direction) gives
rise to Randall-Sundrum type metric with a negative tension brane. However, no
brane source is required. We show that this result is robust under changes in
the discretization scheme. The inclusion of the lapse field gives rise to
solutions whose continuum limit is gauge fixed by the discretization scheme. We
find however one particular scheme which leads to an undetermined lapse
reflecting the reparametrization invariance of the continuum theory. We also
find other solutions, with no continuum counterpart with changes in the metric
signature or avoidance of singularity. We show that the models allow a
continuous mass spectrum for the gravitons with an effective 4D interaction at
small scales. We also discuss some cosmological solutions.Comment: 19 page
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