407 research outputs found
States of quantum systems and their liftings
Let H(1), H(2) be complex Hilbert spaces, H be their Hilbert tensor product
and let tr2 be the operator of taking the partial trace of trace class
operators in H with respect to the space H(2). The operation tr2 maps states in
H (i.e. positive trace class operators in H with trace equal to one) into
states in H(1). In this paper we give the full description of mappings that are
linear right inverse to tr2. More precisely, we prove that any affine mapping
F(W) of the convex set of states in H(1) into the states in H that is right
inverse to tr2 is given by the tensor product of W with some state D in H(2).
In addition we investigate a representation of the quantum mechanical state
space by probability measures on the set of pure states and a representation --
used in the theory of stochastic Schroedinger equations -- by probability
measures on the Hilbert space. We prove that there are no affine mappings from
the state space of quantum mechanics into these spaces of probability measures.Comment: 14 page
The role of infrared divergence for decoherence
Continuous and discrete superselection rules induced by the interaction with
the environment are investigated for a class of exactly soluble Hamiltonian
models. The environment is given by a Boson field. Stable superselection
sectors emerge if and only if the low frequences dominate and the ground state
of the Boson field disappears due to infrared divergence. The models allow
uniform estimates of all transition matrix elements between different
superselection sectors.Comment: 11 pages, extended and simplified proo
Applications of Canonical Transformations
Canonical transformations are defined and discussed along with the
exponential, the coherent and the ultracoherent vectors. It is shown that the
single-mode and the -mode squeezing operators are elements of the group of
canonical transformations. An application of canonical transformations is made,
in the context of open quantum systems, by studying the effect of squeezing of
the bath on the decoherence properties of the system. Two cases are analyzed.
In the first case the bath consists of a massless bosonic field with the bath
reference states being the squeezed vacuum states and squeezed thermal states
while in the second case a system consisting of a harmonic oscillator
interacting with a bath of harmonic oscillators is analyzed with the bath being
initially in a squeezed thermal state.Comment: 14 page
Long-term effects of bilateral pallidal deep brain stimulation in dystonia: a follow-up between 8 and 16Â years
Objective: Observational study to evaluate the long-term motor and non-motor effects of deep brain stimulation (DBS) of the globus pallidus internus (GPi) on medically refractory dystonia.
Background: Dystonia is a chronic disease affecting mainly young patients with a regular life expectancy and lifelong need for therapy. Pallidal DBS is an established treatment for severe isolated dystonia but long-term data are sparse.
Methods: We considered 36 consecutive patients with isolated generalized (nâ=â14) and cervical/segmental (nâ=â22) dystonia operated at CharitĂ©-University Hospital between 2000 and 2007 in a retrospective analysis for long-term outcome of pallidal DBS. In 19 of these patients, we could analyze dystonic symptoms and disability rated by the BurkeâFahnâMarsden Dystonia Rating scale (BFMDRS) at baseline, short-term (ST-FU, range 3â36 months) and long-term follow-up (LT-FU, range 93â197 months). Quality of life and mood were evaluated using the SF36 and Beck Depression Index (BDI) questionnaires.
Results: Patients reached an improvement in motor symptoms of 63.8â±â5.7% (meanâ±âSE) at ST-FU and 67.9â±â6.1% at LT-FU. Moreover, a significant and stable reduction in disability was shown following DBS (54.2â±â9.4% at ST-FU and 53.8â±â9.2% at LT-FU). BDI and SF36 had improved by 40% and 23%, respectively, at LT-FU (nâ=â14). Stimulation-induced adverse events included swallowing difficulties, dysarthria, and bradykinesia. Pulse generator (nâ=â3) and electrodes (nâ=â5) were revised in seven patients due to infection.
Conclusions: Pallidal DBS is a safe and efficacious long-term treatment for dystonia with sustained effects on motor impairment and disability, accompanied by a robust improvement in mood and quality of life
Reduzierung von Missing Wedge Artefakten mit DIRECTT
Wir stellen eine Prozedur vor, mit der typische Missing Wedge MW Artefakte in CT Rekonstruktionen effektiv unterdrĂŒckt werden können. Dazu wird der iterative DIRECTT Algorithmus Direkte Iterative Rekonstruktion Computertomographischer Trajektorien mit einigen Zyklen diskreter Rekonstruk tion eingesetzt. Die Kernfunktionen des Algorithmus , die wiederholte Auswahl und Gewichtung von Elementen einer Zwischenrekonstruktion, werden beibehalten. Abgesehen von SonderfĂ€llen der Röntgen und Neutronentomographie tritt die MW Restriktion neben einer Vielzahl anderer in Standardkonfigurationen der Elektronentomographie auf. Um den MW Effekt isoliert zu untersuchen und beurteilen zu können, werden hier vollstĂ€ndige experimentelle DatensĂ€tze einer bekannten Porenstruktur um einen Sektor beschnitten sowie MW Rekonstruktionen von Porenmodellen erzeugt. Die Ergebnisse werden mit zurzeit verbreiteten Algorithmen Gefilterte RĂŒckprojektion FBP und ART Varianten verglichen. Die Bewertung im Fourierraum zeigt, dass DIRECTT die fehlende Information im MW erfolgreich ergĂ€nzt. Zur quantitativen Bewertung der lokalen Rekonstruktions qualitĂ€t werden Methoden der rĂ€umlichen Statistik eingesetz
How to Open a File and Not Get Hacked
Careless attention to opening files, often caused by prob-lems with path traversal or shared directories, can expose applications to attacks on the file names that they use. In this paper we present criteria to determine if a path is safe from attack and how previous algorithms are not sufficient to protect against such attacks. We then describe an algo-rithm to safely open a file when in the presence of an attack (and how to detect the presence of such an attack), and pro-vide a new library of file open routines that embodies our algorithm. These routines can be used as one-for-one sub-stitutes for conventional POSIX open and fopen calls. 1
X ray Compton Tomography
The potentials of incoherent X ray scattering Compton tomography are investigated. Imaging materials of very different density or atomic number at once is a perpetual challenge for X ray tomography or radiography, in general. In a basic laboratory set up for simultaneous perpendicular Compton scattering and direct beam attenuation tomographic scans are conducted by single channel photon counting. This results in asymmetric distortions of the projection profiles of the scattering CT data set. In a first approach corrections of Compton scattering data by taking advantage of rotational symmetry yield tomograms without major geometric artefacts. A cylindrical sample composed of PE, PA, PVC, glass and wood demonstrates similar Compton contrast for all the substances, while the conventional absorption tomogram only reveals the two high order materials. Comparison to neutron tomography reveals astonishing similarities except for the glass component without hydrogen . Therefore, Compton CT bears the potential to replace neutron tomography, which requires much more efforts
The structure of the quantum mechanical state space and induced superselection rules
The role of superselection rules for the derivation of classical probability
within quantum mechanics is investigated and examples of superselection rules
induced by the environment are discussed.Comment: 11 pages, Standard Latex 2.0
A Feynman-Kac Formula for Anticommuting Brownian Motion
Motivated by application to quantum physics, anticommuting analogues of
Wiener measure and Brownian motion are constructed. The corresponding Ito
integrals are defined and the existence and uniqueness of solutions to a class
of stochastic differential equations is established. This machinery is used to
provide a Feynman-Kac formula for a class of Hamiltonians. Several specific
examples are considered.Comment: 21 page
Longâterm effects of pallidal and thalamic deep brain stimulation in myoclonus dystonia
Objective: Observational study to evaluate long-term effects of deep brain stimulation (DBS) of the globus pallidus internus (GPi) and the ventral intermediate thalamic nucleus (VIM) on patients with medically refractory myoclonus dystonia (MD).
Background: More recently, pallidal as well as thalamic DBS have been applied successfully in MD but long-term data are sparse.
Methods: We retrospectively analyzed a cohort of seven MD patients with either separate (n = 1, VIM) or combined GPi- DBS and VIM-DBS (n = 6). Myoclonus, dystonia and disability were rated at baseline (BL), short-term (ST-FU) and long-term follow-up (LT-FU) using the United Myoclonus Rating Scale, Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS) and Tsui rating scale, respectively. Quality of life (QoL) and mood were evaluated using the SF-36 and Beck Depression Inventory questionnaires, respectively.
Results: Patients reached a significant reduction of myoclonus at ST-FU (62% ± 7.3%; mean ± SE) and LT-FU (68% ± 3.4%). While overall motor BFMDRS changes were not significant at LT-FU, patients with GPi-DBS alone responded better and predominant cervical dystonia ameliorated significantly up to 54% ± 9.7% at long-term. Mean disability scores significantly improved by 44% ± 11.4% at ST-FU and 58% ± 14.8% at LT-FU. Mood and QoL remained unchanged between 5 and up to 20 years postoperatively. No serious long-lasting stimulation-related adverse events were observed.
Conclusions: We present a cohort of MD patients with very long follow-up of pallidal and/or thalamic DBS that supports the GPi as the favourable stimulation target in MD with safe and sustaining effects on motor symptoms (myoclonus>dystonia) and disability
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