6,523 research outputs found
The Unconstitutionality, Ineffectiveness, and Alternatives of Gang Injunctions
Gang violence across America puts in jeopardy the peace and tranquility of neighborhoods. Cities are challenged to keep their communities safe from gang violence. One common way in which cities attempt to combat violent gang activity is by using gang injunctions. Gang injunctions are court orders that prohibit gang members from conducting already-illegal activities such as vandalism, loitering, and use or possession of illegal drugs or weapons within a defined area. These injunctions, however, also prohibit otherwise legal activity such as associating with others within the restricted area of the injunction, using words or hand gestures, and wearing certain clothing. The increased use of gang injunctions to combat violent gang activity is a controversial tactic. The use of gang injunctions raises many constitutional concerns, including violations of the 1st, 4th, 5th, 9th, and 14th amendments. Even if interpreted as constitutional, gang injunctions have been proven ineffective in preventing and deterring gang members from engaging in violent gang activity. Critics believe that gang injunctions create gang cohesiveness, animosity towards the police, and relocate the violent crime created by gang members by pushing gang members into adjacent neighborhoods just outside the injunction\u27s target area. Finally, there are several proven-effective alternatives to gang injunctions. This Note explores the unconstitutionality of gang injunctions, reveals the ineffectiveness of gang injunctions, and investigates more effective and efficient alternatives
Wavefront sensing with a brightest pixel selection algorithm
Astronomical adaptive optics systems with open-loop deformable mirror control
have recently come on-line. In these systems, the deformable mirror surface is
not included in the wavefront sensor paths, and so changes made to the
deformable mirror are not fed back to the wavefront sensors. This gives rise to
all sorts of linearity and control issues mainly centred on one question: Has
the mirror taken the shape requested? Non-linearities in wavefront measurement
and in the deformable mirror shape can lead to significant deviations in mirror
shape from the requested shape. Here, wavefront sensor measurements made using
a brightest pixel selection method are discussed along with the implications
that this has for open-loop AO systems. Discussion includes elongated laser
guide star spots and also computational efficiency.Comment: 10 pages, 12 figures, accepted by MNRA
OPTIMAL PROPENSITY SCORE STRATIFICATION
Stratifying on propensity score in observational studies of treatment is a common technique used to control for bias in treatment assignment; however, there have been few studies of the relative efficiency of the various ways of forming those strata. The standard method is to use the quintiles of propensity score to create subclasses, but this choice is not based on any measure of performance either observed or theoretical. In this paper, we investigate the optimal subclassification of propensity scores for estimating treatment effect with respect to mean squared error of the estimate. We consider the optimal formation of subclasses within formation schemes that require either equal frequency of observations within each subclass or equal variance of the effect estimate within each subclass. Under these restrictions, choosing the partition is reduced to choosing the number of subclasses. We also consider an overalll optimal partition that produces an effect estimate with minimum MSE among all partitions considered. To create this stratification, the investigator must choose both the number of subclasses and their placement. Finally, we present a stratified propensity score analysis of data concerning insurance plan choice and its relation to satisfaction with asthma care
REGRESSION ADJUSTMENT AND STRATIFICATION BY PROPENSTY SCORE IN TREATMENT EFFECT ESTIMATION
Propensity score adjustment of effect estimates in observational studies of treatment is a common technique used to control for bias in treatment assignment. In situations where matching on propensity score is not possible or desirable, regression adjustment and stratification are two options. Regression adjustment is used most often and can be highly efficient, but it can lead to biased results when model assumptions are violated. Validity of the stratification approach depends on fewer model assumptions, but is less efficient than regression adjustment when the regression assumptions hold. To investigate these issues, by simulation we compare stratification and regression adjustments. We consider two stratification approaches; equal frequency classes and an approach the attempts to minimize the mean squared error (MSE) of the treatment effect estimate. The regression approach we consider is a Generalized Additive Model (GAM), that flexibly estimates the relations among propensity score, treatment assignment, and outcome. We find that, under a wide range of plausible data generating distributions, the GAM approach outperforms stratification in treatment effect estimation with respect to bias, variance, and thereby MSE. We illustrate approaches via analysis of data on insurance plan choice and its relation to satisfaction with asthma care
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A pendant proton shuttle on [Fe4N(CO)12]- alters product selectivity in formate vs. H2 production via the hydride [H-Fe4N(CO)12].
Proton relays are known to increase reaction rates for H2 evolution and lower overpotentials in electrocatalytic reactions. In this report we describe two electrocatalysts, [Fe4N(CO)11(PPh3)]- (1-) which has no proton relay, and hydroxyl-containing [Fe4N(CO)11(Ph2P(CH2)2OH)]- (2-). Solid state structures indicate that these phosphine-substituted clusters are direct analogs of [Fe4N(CO)12]- where one CO ligand has been replaced by a phosphine. We show that the proton relay changes the selectivity of reactions: CO2 is reduced selectively to formate by 1- in the absence of a relay, and protons are reduced to H2 under a CO2 atmosphere by 2-. These results implicate a hydride intermediate in the mechanism of the reactions and demonstrate the importance of controlling proton delivery to control product selectivity. Thermochemical measurements performed using infrared spectroelectrochemistry provided pKa and hydricity values for [HFe4N(CO)11(PPh3)]-, which are 23.7, and 45.5 kcal mol-1, respectively. The pKa of the hydroxyl group in 2- was determined to fall between 29 and 41, and this suggests that the proximity of the proton relay to the active catalytic site plays a significant role in the product selectivity observed, since the acidity alone does not account for the observed results. More generally, this work emphasizes the importance of substrate delivery kinetics in determining the selectivity of CO2 reduction reactions that proceed through metal-hydride intermediates
Non Abelian Geometrical Tachyon
We investigate the dynamics of a pair of coincident D5 branes in the
background of NS5 branes. It has been proposed by Kutasov that the system
with a single probing D-brane moving radially in this background is dual to the
tachyonic DBI action for a non-BPS Dp brane. We extend this proposal to the
non-abelian case and find that the duality still holds provided one promotes
the radial direction to a matrix valued field associated with a non-abelian
geometric tachyon and a particular parametrization for the transverse scalar
fields is chosen. The equations of motion of a pair of coincident D5 branes
moving in the NS5 background are determined. Analytic and numerical solutions
for the pair are found in certain simplified cases in which the U(2) symmetry
is broken to corresponding to a small transverse separation
of the pair. For certain range of parameters these solutions describe periodic
motion of the centre of mass of the pair 'bouncing off' a finite sized throat
whose minimum size is limited by the D5 branes separation.Comment: 18 pages, 2 figures, PdfLatex: references added.accepted for
publication in JHE
Spin transfer switching of spin valve nanopillars using nanosecond pulsed currents
Spin valve nanopillars are reversed via the mechanism of spin momentum
transfer using current pulses applied perpendicular to the film plane of the
device. The applied pulses were varied in amplitude from 1.8 mA to 7.8 mA, and
varied in duration within the range of 100 ps to 200 ns. The probability of
device reversal is measured as a function of the pulse duration for each pulse
amplitude. The reciprocal pulse duration required for 95% reversal probability
is linearly related to the pulse current amplitude for currents exceeding 1.9
mA. For this device, 1.9 mA marks the crossover between dynamic reversal at
larger currents and reversal by thermal activation for smaller currents
Fuzzy Sphere Dynamics and Non-Abelian DBI in Curved Backgrounds
We consider the non-Abelian action for the dynamics of -branes in the
background of -branes, which parameterises a fuzzy sphere using the SU(2)
algebra. We find that the curved background leads to collapsing solutions for
the fuzzy sphere except when we have branes in the background, which
is a realisation of the gravitational Myers effect. Furthermore we find the
equations of motion in the Abelian and non-Abelian theories are identical in
the large limit. By picking a specific ansatz we find that we can
incorporate angular momentum into the action, although this imposes restriction
upon the dimensionality of the background solutions. We also consider the case
of non-Abelian non-BPS branes, and examine the resultant dynamics using
world-volume symmetry transformations. We find that the fuzzy sphere always
collapses but the solutions are sensitive to the combination of the two
conserved charges and we can find expanding solutions with turning points. We
go on to consider the coincident 5-brane background, and again construct
the non-Abelian theory for both BPS and non-BPS branes. In the latter case we
must use symmetry arguments to find additional conserved charges on the
world-volumes to solve the equations of motion. We find that in the Non-BPS
case there is a turning solution for specific regions of the tachyon and radion
fields. Finally we investigate the more general dynamics of fuzzy
in the -brane background, and find collapsing solutions
in all cases.Comment: 49 pages, 3 figures, Latex; Version to appear in JHE
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