610 research outputs found
Spin-Exchange Cross Section for Electron Excitation of Na 3S 3P Determined by a Novel Spectroscopic Technique
An experimental technique is described which enables determination of the partial cross sections for electron excitation of atoms as a function of changes in spin and orbital angular momentum. This method provides a good signal-to-noise ratio in the energy region near threshold, and could be used to study long- or short-lived excited states of many atomic systems. Measurements for Na 3S−3P, near-threshold excitation are reported here. The results are generally in good agreement with the close-coupling calculations of D. L. Moores and D. W. Norcross [J. Phys. B 5, 1482 (1972)] for the largest ΔmS and ΔmL components of the cross section, but not for the component with |ΔmS|=1 and |ΔmL|=1, indicating that the exchange interaction is larger than previously recognized
Differential, Partial Cross Sections for Electron Excitation of the Sodium 3P State
Using a powerful laser-based experimental method, the cross section for electron excitation of Na(3S) atoms to the Na(3P) state has been decomposed into partial components with respect to changes in the spin and angular momentum of the atomic electron, and these partial cross sections are further reduced to their differential character with respect to the electron scattering angle. Partial, differential cross sections are reported for electron collision energies from threshold 2.1 to 3.6 eV, and compared to available calculations
On-shell supersymmetry for massive multiplets
The consequences of on-shell supersymmetry are studied for scattering
amplitudes with massive particles in four dimensions. Using the massive version
of the spinor helicity formalism the supersymmetry transformations relating
products of on-shell states are derived directly from the on-shell
supersymmetry algebra for any massive representation. Solutions to the
resulting Ward identities can be constructed as functions on the on-shell
superspaces that are obtained from the coherent state method. In simple cases
it is shown that these superspaces allow one to construct explicitly
supersymmetric scattering amplitudes. Supersymmetric on-shell recursion
relations for tree-level superamplitudes with massive particles are introduced.
As examples, simple supersymmetric amplitudes are constructed in SQCD, the
Abelian Higgs model, the Coulomb branch of N=4 super Yang-Mills, QCD with an
effective Higgs-gluon coupling and for massive vector boson currents.Comment: 49+9 pages, 4 figures, v2: references updated, typos corrected,
examples added, v3: final PRD versio
First Experiments on Stochastic Cooling of Heavy Ion Beams at the ESR
At the experimental storage ring ESR of GSI, one half of the foreseen pick-up and kicker tanks are installed, the rest will follow in 1998. First experimental tests of the stochastic precooling system have been performed since April 1997. Longitudinal Palmer cooling was successfully demonstrated. E-folding cooling times of 8.6 seconds were determined with carbon beams. No significant dependence of the cooling time on the number of particles was observed during these first tests. This may be explained by a low signal to noise ratio of the signals obtained from the pick-ups in the present configuration. With heavy ions in higher charge states faster cooling times are expected. The experiments are an important step towards the realization of experiments with radioactive fragments, e.g. in order to measure nuclear masses or half-lives of stripped exotic ions
On-shell recursion relations for all Born QCD amplitudes
We consider on-shell recursion relations for all Born QCD amplitudes. This
includes amplitudes with several pairs of quarks and massive quarks. We give a
detailed description on how to shift the external particles in spinor space and
clarify the allowed helicities of the shifted legs. We proof that the
corresponding meromorphic functions vanish at z --> infinity. As an application
we obtain compact expressions for helicity amplitudes including a pair of
massive quarks, one negative helicity gluon and an arbitrary number of positive
helicity gluons.Comment: 30 pages, minor change
OS ATAQUES ÀS CORTES CONSTITUCIONAIS E A INTERPRETAÇÃO IRRESTRITA DO DIREITO COMO SINTOMAS DO AUTORITARISMO CONTEMPORÂNEO
O tema do presente trabalho é o alargamento da interpretação do direito por parte do Poder Judiciário, que tem se valido da opinião pública para subverter garantias constitucionais, sendo que o próprio Tribunal Constitucional quando se posiciona no sentido de proteger tais garantias, tem sido alvo de ataques do público e de outras instituições. Como objetivos, destacam-se a análise da relação entre constitucionalismo e democracia; do ativismo judicial desmedido como sintoma do autoritarismo presente em instituições como o Poder Judiciário e o questionamento sobre a possibilidade de a democracia no Brasil estar em declÃnio. A metodologia utilizada é a revisão bibliográfica, baseada em autores que têm contribuÃdo com o tema das teorias da democracia, e da atual situação brasileira. Também se vale de notÃcias de jornal, uma vez que a situação de diferentes regimes (aparentemente) democráticos têm ocupado as manchetes dos jornais e portais de notÃcias. Uma das conclusões do trabalho é de que a democracia brasileira encontra-se em crise, e que apesar da normalidade aparente em que se encontram as instituições, é possÃvel considerar que o paÃs está imerso em um estado de exceção, sobretudo judicial.Palavras-chave: Ativismo judicial. Constitucionalismo. Democracia. Estado de exceção
Fast Stochastic Cooling of Heavy Ions at the ESR Storage Ring
Since the completion of the installation of pick-up and kicker tanks in the ESR, stochastic cooling in all phase space dimensions has been demonstrated with rather short cooling times. New RF components were added. The system is now ready for experiments with secondary beams. The momentum sensitivity of the pick-up electrodes was measured. The ability of the Palmer cooling system to cool beams with a maximum momentum spread of ± 0.7 % was demonstrated. After injecting an uncooled primary argon beam from the SIS synchrotron, e-folding cooling times of 0.86 s in the longitudinal phase plane and 1.6 s in the horizontal plane were measured with 5×106 injected particles. These values are close to theoretical expectations. In a first experiment with uranium, the shortest cooling times have been below 0.5 s in both the longitudinal and vertical phase planes. The system cools the complete injected beam without beam loss. An experiment with beam accumulation following stochastic precooling was performed successfully. The resulting equilibrium phase space densities are high enough to be followed by fast electron cooling of the stack
Stochastic Cooling at the ESR
Stochastic precooling at the ESR storage ring of GSI will be used mainly for experiments with stored radioactive fragment beams. They arrive from the fragment separator with momentum spreads and emittances for which electron cooling is too slow. The installation of components at the ESR is now complete and first commissioning experiments have been performed. Both longitudinal and transverse stochastic cooling have been demonstrated. The paper gives a short account of the system architecture, and of the response of quarter-wave plates and superelectrodes at intermediate energies. The preparation of fragment beams suitable for subsequent electron cooling is discussed for the case that a mixture of different ion species is present in the cooler ring. Results of commissioning and future prospects are presented
Contrastive Language-Image Pretrained Models are Zero-Shot Human Scanpath Predictors
Understanding the mechanisms underlying human attention is a fundamental
challenge for both vision science and artificial intelligence. While numerous
computational models of free-viewing have been proposed, less is known about
the mechanisms underlying task-driven image exploration. To address this gap,
we present CapMIT1003, a database of captions and click-contingent image
explorations collected during captioning tasks. CapMIT1003 is based on the same
stimuli from the well-known MIT1003 benchmark, for which eye-tracking data
under free-viewing conditions is available, which offers a promising
opportunity to concurrently study human attention under both tasks. We make
this dataset publicly available to facilitate future research in this field. In
addition, we introduce NevaClip, a novel zero-shot method for predicting visual
scanpaths that combines contrastive language-image pretrained (CLIP) models
with biologically-inspired neural visual attention (NeVA) algorithms. NevaClip
simulates human scanpaths by aligning the representation of the foveated visual
stimulus and the representation of the associated caption, employing
gradient-driven visual exploration to generate scanpaths. Our experimental
results demonstrate that NevaClip outperforms existing unsupervised
computational models of human visual attention in terms of scanpath
plausibility, for both captioning and free-viewing tasks. Furthermore, we show
that conditioning NevaClip with incorrect or misleading captions leads to
random behavior, highlighting the significant impact of caption guidance in the
decision-making process. These findings contribute to a better understanding of
mechanisms that guide human attention and pave the way for more sophisticated
computational approaches to scanpath prediction that can integrate direct
top-down guidance of downstream tasks
High precision fundamental constants at the TeV scale
This report summarizes the proceedings of the 2014 Mainz Institute for
Theoretical Physics (MITP) scientific program on "High precision fundamental
constants at the TeV scale". The two outstanding parameters in the Standard
Model dealt with during the MITP scientific program are the strong coupling
constant and the top-quark mass . Lacking knowledge on the
value of those fundamental constants is often the limiting factor in the
accuracy of theoretical predictions. The current status on and
has been reviewed and directions for future research have been identified.Comment: 57 pages, 24 figures, pdflate
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