12,787 research outputs found
Juvenile Detention Alternatives Initiative, Zero-Tolerance Discipline, and the School-to Prison Pipeline
Zero-tolerance discipline policies led to the introduction of police on school campuses and have resulted in a disproportionate number of in-school arrests and referrals of Black middle-school students, subjecting them to the school-to-prison pipeline. Data shows the negative effects of zero tolerance; however, less is known regarding alternative evidence-based strategies such as the Juvenile Detention Alternatives Initiative (JDAI). Grounded in the labeling theoretical framework, this study examined whether JDAI status (pre-JDAI and post-JDAI) could predict arrests and referrals while controlling for race, gender, and age. Secondary data were collected from a juvenile court in northwest Georgia on 1,303 middle-school students. The students who formed this purposive sample for the study were arrested or referred 2 years prior to the implementation of the JDAI School Referral Reduction Program and 2 recent years post-JDAI. Binary logistic regressions were conducted for each of the outcomes of arrests and referrals to ascertain the predictive relationships of JDAI, race, gender, and age. The results found only gender and age to be significant predictors of arrests and referrals. However, additional findings reported Black students were 89.4% of the students arrested or referred to the juvenile court, and 93.2% of those arrests and referrals occurred during the 2-year period pre-JDAI. This research is significant for stakeholders involved in education and juvenile justice reform who want to positively effect social change through the use of programs and policies that narrow the academic achievement gap and reduce the disproportionate number of Black students’ contact with the criminal justice system
Temperature dependent graphene suspension due to thermal Casimir interaction
Thermal effects contributing to the Casimir interaction between objects are
usually small at room temperature and they are difficult to separate from
quantum mechanical contributions at higher temperatures. We propose that the
thermal Casimir force effect can be observed for a graphene flake suspended in
a fluid between substrates at the room temperature regime. The properly chosen
materials for the substrates and fluid induce a Casimir repulsion. The balance
with the other forces, such as gravity and buoyancy, results in a stable
temperature dependent equilibrium separation. The suspended graphene is a
promising system due to its potential for observing thermal Casimir effects at
room temperature.Comment: 5 pages, 4 figures, in APL production 201
Magnetars' Giant Flares: the case of SGR 1806-20
We first review on the peculiar characteristics of the bursting and flaring
activity of the Soft Gamma-ray Repeaters and Anomalous X-ray Pulsars. We then
report on the properties of the SGR 1806-20's Giant Flare occurred on 2004
December 27th, with particular interest on the pre and post flare
intensity/hardness correlated variability. We show that these findings are
consistent with the picture of a twisted internal magnetic field which stresses
the star solid crust that finally cracks causing the giant flare (and the
observed torsional oscillations). This crustal fracturing is accompanied by a
simplification of the external magnetic field with a (partial) untwisting of
the magnetosphere.Comment: 6 pages, 2 figures; accepted for publication in the Chinese Journal
for Astronomy and Astrophysics (Vulcano conference - 2005
A general framework for consistent logical reasoning in Wigner's friend scenarios: subjective perspectives of agents within a single quantum circuit
It is natural to expect a complete physical theory to have the ability to
consistently model agents as physical systems of the theory. In [Nat. Comms. 9,
3711 (2018)], Frauchiger and Renner (FR) claim to show that when agents in
quantum theory reason about each other's knowledge in a certain Wigner's friend
scenario, they arrive at a logical contradiction. In light of this, Renner
often poses the challenge: provide a set of reasoning rules that can be used to
program quantum computers that may act as agents, which are (a) logically
consistent (b) generalise to arbitrary Wigner's friend scenarios (c)
efficiently programmable and (d) consistent with the temporal order of the
protocol. Here we develop a general framework where we show that every logical
Wigner's friend scenario (LWFS) can be mapped to a single temporally ordered
quantum circuit, which allows agents in any LWFS to reason in a way that meets
all four criteria of the challenge. Importantly, our framework achieves this
general resolution without modifying classical logic or unitary quantum
evolution or the Born rule, while allowing agents' perspectives to be
fundamentally subjective. We analyse the FR protocol in detail, showing how the
apparent paradox is resolved there. We show that apparent logical
contradictions in any LWFS only arise when ignoring the choice of Heisenberg
cut in scenarios where this choice does matter, and taking this dependence into
account will always resolve the apparent paradox. Our results establish that
universal applicability of quantum theory does not pose any threat to
multi-agent logical reasoning and we discuss the implications of these results
for FR's no-go theorem. Moreover, our formalism suggests the possibility of a
truly relational and operational description of Wigner's friend scenarios that
is consistent with quantum theory as well as probability theory applied to
measurement outcomes.Comment: 33 + 14 pages, 10 figure
Normal ground state of dense relativistic matter in a magnetic field
The properties of the ground state of relativistic matter in a magnetic field
are examined within the framework of a Nambu-Jona-Lasinio model. The main
emphasis of this study is the normal ground state, which is realized at
sufficiently high temperatures and/or sufficiently large chemical potentials.
In contrast to the vacuum state, which is characterized by the magnetic
catalysis of chiral symmetry breaking, the normal state is accompanied by the
dynamical generation of the chiral shift parameter . In the chiral
limit, the value of determines a relative shift of the longitudinal
momenta (along the direction of the magnetic field) in the dispersion relations
of opposite chirality fermions. We argue that the chirality remains a good
approximate quantum number even for massive fermions in the vicinity of the
Fermi surface and, therefore, the chiral shift is expected to play an important
role in many types of cold dense relativistic matter, relevant for applications
in compact stars. The qualitative implications of the revealed structure of the
normal ground state on the physics of protoneutron stars are discussed. A
noticeable feature of the parameter is that it is insensitive to
temperature when , where is the chemical potential, and
{\it increases} with temperature for . The latter implies that the
chiral shift parameter is also generated in the regime relevant for heavy ion
collisions.Comment: 28 pages, 6 figures; v2: title changed in journa
Variability in GRBs - A Clue
We show that external shocks cannot produce a variable GRB, unless they are
produced by an extremely narrow jets (angular opening of < ~10^{-4}) or if only
a small fraction of the shell emits the radiation and the process is very
inefficient. Internal shocks can produce the observed complex temporal
structure provided that the source itself is variable. In this case, the
observed temporal structure reflects the activity of the ``inner engine'' that
drives the bursts. This sets direct constraints on it.Comment: 15 page latex file with 5 PS figure. Complete uuencoded compressed PS
file is available at ftp://shemesh.fiz.huji.ac.il or at
http://shemesh.fiz.huji.ac.il/papers/SaP_aclue.u
The 2009 outburst of magnetar 1E 1547-5408: Persistent radiative and burst properties
The magnetar 1E~15475408 recently exhibited two periods of outburst,
beginning on 2008 October 3 and 2009 January 22. Here we present an analysis of
the persistent radiative evolution and a statistical study of the burst
properties during the 2009 outburst using the {\em Swift} X-ray Telescope
(XRT). We find that the 1--10 keV flux increased by a factor of and
hardened significantly, peaking hours after the onset of the outburst.
The observed pulsed fraction exhibited an anti-correlation with phase-averaged
flux. Properties of the several hundred X-ray bursts during the 2009 outburst
were determined and compared to those from other magnetar outburst events. We
find that the peaks of the bursts occur randomly in phase but that the folded
counts that compose the bursts exhibit a pulse which is misaligned with the
persistent pulse phase. We also report a correlation between burst hardness and
flux. We compare the hardness-flux evolution of the persistent emission of both
outbursts to those from other magnetars and find that although there does exist
an overall trend, the degree of hardening for a given increase in flux is not
uniform from source to source. These results are discussed in the context of
previous results and within the magnetar model.Comment: 10 pages, 9 figures. Accepted for publication in Ap
Sustainable valorisation of organic urban wastes : insights from African case studies
Understanding the problems and potentials of the organic waste stream is perhaps the single most important step that city authorities in Africa could take in moving towards sustainable, affordable, effective and efficient waste management. This publication presents four examples of recent attempts to manage organic waste sustainably in the African context. The participants in the ‘Nairobi organic urban waste’ project have structured this case exercise in order to use the case studies as object lessons, to harvest genuine insights into the feasibility of a variety of ways to successfully and sustainably valorise urban organic waste streams. Three contemporary case examples of compost production are presented. These include composting by a community-based organisation in the Kenyan private sector and by a public-private partnership in Malawi. In all three cases, the project and case study focus is on the relations between city waste and the agricultural supply chain. A fourth case study describes the technical and economic potential to produce and use biogas from urban organic waste
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