74 research outputs found
Convergence of CI single center calculations of positron-atom interactions
The Configuration Interaction (CI) method using orbitals centered on the
nucleus has recently been applied to calculate the interactions of positrons
interacting with atoms. Computational investigations of the convergence
properties of binding energy, phase shift and annihilation rate with respect to
the maximum angular momentum of the orbital basis for the e^+Cu and PsH bound
states, and the e^+-H scattering system were completed. The annihilation rates
converge very slowly with angular momentum, and moreover the convergence with
radial basis dimension appears to be slower for high angular momentum. A number
of methods of completing the partial wave sum are compared, an approach based
on a Delta X_J = a/(J + 1/2)^n + b/(J + 1/2)^(n+1) form (with n = 4 for phase
shift (or energy) and n = 2 for the annihilation rate) seems to be preferred on
considerations of utility and underlying physical justification.Comment: 23 pages preprint RevTeX, 11 figures, submitted to PR
A systematic review of brain imaging findings in neurological infection with Japanese encephalitis virus compared with Dengue virus.
OBJECTIVES: Japanese encephalitis virus (JEV) and dengue virus (DENV) represent important causes of encephalitis in Asia. Brain imaging may provide diagnostic clues about the etiology of infectious encephalitis. We performed a systematic review of brain imaging findings in Japanese encephalitis (JE) and DENV neurological infection (dengue) to identify characteristic lesions. METHODOLOGY: Five databases were searched. We included all study types and imaging techniques. Laboratory methods were categorized using diagnostic confidence levels. Imaging data were synthesized, and focal findings are presented as proportions for JE and dengue and for subgroups based on diagnostic confidence. PRINCIPAL FINDINGS: Thalamic lesions were the most reported magnetic resonance imaging finding in both diseases but appeared to occur more often in JE (74% in 23 studies) than dengue (29.4% in 58 studies). In cases diagnosed with antigen or nucleic acid tests, thalamic lesions were reported frequently in both JE (76.5% in 17 studies) and dengue (65.2% in 23 studies). SIGNIFICANCE: The results suggest that thalamic lesions frequently occur in both JE and dengue encephalitis. No radiological findings were found to be pathognomonic of either disease. Although brain imaging may support a diagnosis, laboratory confirmation with highly specific tests remains crucial
K^+ -> pi^+pi^0e^+e^-: a novel short-distance probe
We study the decay K^+ -> pi^+ pi^0 e^+ e^-, currently under analysis by the
NA62 Collaboration at CERN. In particular, we provide a detailed analysis of
the Dalitz plot for the long-distance, gamma^*-mediated, contributions
(Bremsstrahlung, direct emission and its interference). We also examine a set
of asymmetries to isolate genuine short-distance effects. While we show that
charge asymmetries are not required to test short distances, they provide the
best environment for its detection. This constitutes by itself a strong
motivation for NA62 to study K^- decays in the future. We therefore provide a
detailed study of different charge asymmetries and the corresponding estimated
signals. Whenever possible, we make contact with the related processes K^+ ->
pi^+ pi^0 gamma and K_L -> pi^+ pi^- e^+ e^- and discuss the advantages of K^+
-> pi^+ pi^0 e^+ e^- over them.Comment: 25 pages, 6 figure
Scattering phase shift for relativistic exponential-type separable potentials
The J-matrix method of scattering is used to obtain analytic expressions for
the phase shift of two classes of relativistic exponential-type separable
potentials whose radial component is either of the general form r^(n-1)exp(-r)
or r^(2n)exp(-r^2), where n = 0, 1, or 2. The rank of these separable
potentials is n + 1. The nonrelativistic limit is obtained and shown to be
identical to the nonrelativistic phase shift. An exact numerical evaluation for
higher order potentials (n > 2) can also be obtained in a simple way as
illustrated for the case n = 3.Comment: Accepted for publication in J. Phys. A, to appear in January 2002.
Replaced with a more portable PDF versio
Ethical, legal and social aspects of human cerebral organoids and their governance in Germany, the United Kingdom and the United States
Hamburg's Spaces of Danger: Race, Violence and Memory in a Contemporary Global City
Germany today is experiencing the strongest upsurge of right-wing populism since the second world war, most notably with the rise of Pegida and Alternative fĂŒr Deutschland. Yet wealthy global cities like Hamburg continue to present themselves as the gatekeepers of liberal progress and cosmopolitan openness. This article argues that Hamburgâs urban boosterism relies on, while simultaneously obscuring, the same structures of racial violence that embolden reactionary movements. Drawing on the work of Walter Benjamin and Allan Pred, we present an archaeology of Hamburgâs landscape, uncovering some of its âspaces of dangerâââsites layered with histories of violence, many of which lie buried and forgotten. We find that these spaces, when they become visible, threaten to undermine Hamburgâs cosmopolitan narrative. They must, as a result, be continually erased or downplayed in order to secure the city as an attractive site for capital investment. To illustrate this argument, we give three historical examples: Hamburgâs role in the Hanseatic League during the medieval and early modern period; the city under the Nazi regime; and the recent treatment of Black African refugees. The articleâs main contribution is to better situate issues of historical landscape, collective memory and racialized violence within the political economy of todayâs global city
Unraveling the temperature dependence of the yield strength in single-crystal tungsten using atomistically-informed crystal plasticity calculations
We use a physically-based crystal plasticity model to predict the yield
strength of body-centered cubic (bcc) tungsten single crystals subjected to
uniaxial loading. Our model captures the thermally-activated character of screw
dislocation motion and full non-Schmid effects, both of which are known to play
a critical role in bcc plasticity. The model uses atomistic calculations as the
sole source of constitutive information, with no parameter fitting of any kind
to experimental data. Our results are in excellent agreement with experimental
measurements of the yield stress as a function of temperature for a number of
loading orientations. The validated methodology is then employed to calculate
the temperature and strain-rate dependence of the yield strength for 231
crystallographic orientations within the standard stereographic triangle. We
extract the strain-rate sensitivity of W crystals at different temperatures,
and finish with the calculation of yield surfaces under biaxial loading
conditions that can be used to define effective yield criteria for engineering
design models
CP-violation in K_{S,L}->\pi^{+}\pi^{-}\gamma and K_{S,L}->\pi^{+}\pi^{-}e^{+}e^{-} decays
The dependence of K_{S,L}->\pi^{+}\pi^{-}\gamma decay probabilities on photon
polarization is calculated. The phases of terms of amplitude that arise from
the pion-pion interaction are obtained by using a simple realistic model of
pion-pion interaction via virtual \rho-meson, instead of the ChPT. The results
are compared with those of other authors and the origin of slight discrepancies
is explained. It is shown that the standard ChPT approach for K_{S,L}->
\pi^{+}\pi^{-}\gamma decays cannot reproduce the contribution of the \rho-meson
to the P-wave \pi\pi interaction. The departure of the photon spectrum from
pure bremsstrahlung due to the pion loop contribution to the direct emission
amplitude is calculated. It is shown that the interference between the terms of
amplitude with different CP-parity appears only when the photon is polarized
(linearly or circularly). Instead of measuring the linear polarization, the
angular correlation between the \pi^{+}\pi^{-} and e^{+}e^{-} planes in
K_{S,L}->\pi^{+}\pi^{-}e^{+}e^{-} decay can be studied.Comment: 32 pages, 10 figures, 1 table, LaTex ; added figure, the comparison
with ChPT revise
Ethical, legal and social aspects of human cerebral organoids and their governance in Germany, the United Kingdom and the United States
Human cerebral organoids (HCOs) are model systems that enable researchers to investigate the human brain in ways that had previously been impossible. The emergence of HCOs was accompanied by both expert and layperson discussions concerning the possibility of these novel entities developing sentience or consciousness. Such concerns are reflected in deliberations about how to handle and regulate their use. This perspective article resulted from an international and interdisciplinary research retreat âEthical, Legal and Social Aspects of Human Cerebral Organoids and their Governance in Germany, the United Kingdom and the United Statesâ, which took place in TĂŒbingen, Germany, in August 2022. The retreat focused on whether HCO research requires new ethical and regulatory approaches. It addressed epistemic issues around the detection and theorisation of consciousness, ethical concerns around moral status and research conduct, difficulties for legislation and guidelines managing these entities, and public engagement
First observation and study of the K± â ϱÏ0e+eâ decay
The NA48/2 experiment at CERN reports the first observation of the K±âϱÏ0e+eâ decay from an exposure of 1.7Ă1011 charged kaon decays recorded in 2003-2004. A sample of 4919 candidates with 4.9% background contamination allows the determination of the branching ratio in the full kinematic region, BR(K±âϱÏ0e+eâ)=(4.24±0.14)Ă10â6. The study of the kinematic space shows evidence for a structure dependent contribution in agreement with predictions based on chiral perturbation theory. Several P- and CP-violating asymmetries are also evaluated
- âŠ