1,040 research outputs found
Medizinische Anwendungsfelder des Lasers in Gegenwart und Zukunft
In den letzten Jahren hat der Laser in einer Reihe von Fachgebieten seinen festen Platz erworben, z.B. in der Ophthalmologie, Dermatologie, Neurochirurgie, HNO, Pulmologie, Gastroenterologie, Allgemeine Chirurgie, Urologie, GynĂ€kologie und OrthopĂ€die. Entsprechend den gewĂŒnschten Problemlösungen mĂŒssen die QualitĂ€ten der jeweils unterschiedlichen Lasersysteme herangezogen werden.
Der Argon Laser wird wegen seiner hohen SelektivitĂ€t fĂŒr körpereigene Chromophore in der Ophthalmologie und Dermatologie benutzt.
Der CO2 Laser ist wegen seiner hohen Wasserabsorption und damit geringen Eindringtiefe in das Gewebe ein sehr exaktes Schneidinstrument. Er findet ĂŒberall dort Verwendung, wo mikrochirurgisches Arbeiten bzw. flĂ€chenhaftes Abtragen gefordert ist. Sein Nachteil ist die zur Zeit fehlende Transmission der Strahlung ĂŒber Fasern.
Der Nd:YAG Laser ist ein typischer Volumenkoagulator und wird ĂŒberall dort eingesetzt, wo gefĂ€Ăreiche Strukturen wie Fehlbildungen und Tumore vorliegen. Seine Ăbertragbarkeit durch Glasfasern gestattet eine universelle Anwendung. Ăber flexible oder starre Endoskope kann er zur Koagulation von Blutungen, bei höherer Leistung zur Rekanalisation von Tumorstenosen benutzt werden. Mit einem FokussierhandstĂŒck und entsprechend hoher Leistungsdichte sind Resektionen an parenchymatösen Organen bei gleichzeitig guter HĂ€mostase möglich
Anisotropic Quantum Spin Chains
We have studied two models for anisotropic quantum spin chains. (i) XYâchain with a field in the plane: The magnetization of the ferromagnet behaves as h1/3 for small fields, in agreement with scaling laws. The antiferromagnet shows a critical field at which the ground state is a simple NĂ©el state and which separates power law from exponential decay of spatial correlations. (ii) Anisotropic XYâchain: The dynamic zâcomponent spin correlation function can be decomposed into a spin wave and a soliton contribution. The nature of quantum soliton excitations is studied and their form compared to soliton solutions of classical equations of motion
Thermodynamics of ideal quantum gas with fractional statistics in D dimensions
We present exact and explicit results for the thermodynamic properties
(isochores, isotherms, isobars, response functions, velocity of sound) of a
quantum gas in dimensions D>=1 and with fractional exclusion statistics 0<=g<=1
connecting bosons (g=0) and fermions (g=1). In D=1 the results are equivalent
to those of the Calogero-Sutherland model. Emphasis is given to the crossover
between boson-like and fermion-like features, caused by aspects of the
statistical interaction that mimic long-range attraction and short-range
repulsion. The full isochoric heat capacity and the leading low-T term of the
isobaric expansivity in D=2 are independent of g. The onset of Bose-Einstein
condensation along the isobar occurs at a nonzero transition temperature in all
dimensions. The T-dependence of the velocity of sound is in simple relation to
isochores and isobars. The effects of soft container walls are accounted for
rigorously for the case of a pure power-law potential.Comment: 15 pages, 31 figure
Electrical control of inter-dot electron tunneling in a quantum dot molecule
We employ ultrafast pump-probe spectroscopy to directly monitor electron
tunneling between discrete orbital states in a pair of spatially separated
quantum dots. Immediately after excitation, several peaks are observed in the
pump-probe spectrum due to Coulomb interactions between the photo-generated
charge carriers. By tuning the relative energy of the orbital states in the two
dots and monitoring the temporal evolution of the pump-probe spectra the
electron and hole tunneling times are separately measured and resonant
tunneling between the two dots is shown to be mediated both by elastic and
inelastic processes. Ultrafast (< 5 ps) inter-dot tunneling is shown to occur
over a surprisingly wide bandwidth, up to ~8 meV, reflecting the spectrum of
exciton-acoustic phonon coupling in the system
Dynamical Properties of Quantum Spin Systems in Magnetically Ordered Product Ground States
The oneâdimensional spinâs XYZmodel in a magnetic field of particular strength has a ferroâ or antiferromagnetically ordered product ground state. The recursion method is employed to determine T=0 dynamic structure factors for systems with s=1/2, 1, 3/2. The line shapes and peak positions differ significantly from the corresponding spinâwave results, but their development for increasing values of s suggests a smooth extrapolation to the spinâwave picture
Interaction and thermodynamics of spinons in the XX chain
The mapping between the fermion and spinon compositions of eigenstates in the
one-dimensional spin-1/2 XX model on a lattice with N sites is used to describe
the spinon interaction from two different perspectives: (i) For finite N the
energy of all eigenstates is expressed as a function of spinon momenta and
spinon spins, which, in turn, are solutions of a set of Bethe ansatz equations.
The latter are the basis of an exact thermodynamic analysis in the spinon
representation of the XX model. (ii) For N -> infinity the energy per site of
spinon configurations involving any number of spinon orbitals is expressed as a
function of reduced variables representing momentum, filling, and magnetization
of each orbital. The spins of spinons in a single orbital are found to be
coupled in a manner well described by an Ising-like equivalent-neighbor
interaction, switching from ferromagnetic to antiferromagnetic as the filling
exceeds a critical level. Comparisons are made with results for the
Haldane-Shastry model.Comment: 16 pages, 3 figure
Quasiparticles governing the zero-temperature dynamics of the 1D spin-1/2 Heisenberg antiferromagnet in a magnetic field
The T=0 dynamical properties of the one-dimensional (1D)
Heisenberg antiferromagnet in a uniform magnetic field are studied via Bethe
ansatz for cyclic chains of sites. The ground state at magnetization
, which can be interpreted as a state with spinons or as a
state of magnons, is reconfigured here as the vacuum for a different
species of quasiparticles, the {\em psinons} and {\em antipsinons}. We
investigate three kinds of quantum fluctuations, namely the spin fluctuations
parallel and perpendicular to the direction of the applied magnetic field and
the dimer fluctuations. The dynamically dominant excitation spectra are found
to be sets of collective excitations composed of two quasiparticles excited
from the psinon vacuum in different configurations. The Bethe ansatz provides a
framework for (i) the characterization of the new quasiparticles in relation to
the more familiar spinons and magnons, (ii) the calculation of spectral
boundaries and densities of states for each continuum, (iii) the calculation of
transition rates between the ground state and the dynamically dominant
collective excitations, (iv) the prediction of lineshapes for dynamic structure
factors relevant for experiments performed on a variety of quasi-1D
antiferromagnetic compounds, including KCuF,
Cu(CHN, and CuGeO.Comment: 13 pages, 12 figure
Recursion Method in Quantum Spin Dynamics: The Art of Terminating a Continued Fraction
The results obtained from applications of the recursion method to quantum manyâbody dynamics can be greatly improved if an appropriate termination function is employed in the continuedâfraction representation of the corresponding relaxation function. We present a general recipe for the construction and use of such termination functions along with two applications in spin dynamics. The method can be adapted to any other problem in quantum manyâbody dynamics
First evidence of vertical Hepatozoon canis transmission in dogs in Europe
Background
Hepatozoon canis is a protozoal agent that is known to be transmitted by oral uptake of H. canis-infected Rhipicephalus sanguineus sensu lato ticks in dogs. Vertical transmission of H. canis has only been described once in a study evaluating dogs from Japan. The aim of this study was to investigate the parasitological status of puppies from a bitch that had tested positive for Hepatozoon spp. prior to giving birth.
Findings
A 4-year-old, female, pregnant dog imported from Italy (Sardinia) to Germany showed clinical signs of lethargy and tachypnoea and tested positive for H. canis by PCR. The dog gave birth to eight puppies, one of which was stillborn and another that had to be reanimated. Haematology, buffy coat analysis and a biochemistry profile were performed for each dog. EDTA-blood of the surviving seven puppies and bone marrow, liver, spleen, amniotic fluid, and umbilical cord of the stillborn puppy was tested for the presence of Hepatozoon spp. by PCR.
The mother and the seven surviving puppies tested positive for H. canis by PCR at day 62 post-partum. Gamonts were detected in all dogs by buffy coat evaluation. Haematological and biochemistry results revealed mild abnormalities. In the stillborn puppy, spleen, umbilical cord, and amniotic fluid were positive for H. canis.
Conclusion
The results confirm that vertical transmission is a possible route of H. canis infection in dogs, demonstrated by molecular detection of the pathogen in the stillborn puppy. In the seven surviving puppies, vertical transmission was the most likely transmission route. A potential impact of the level of parasitaemia on the health of puppies, as well as its pathogenesis, should be investigated further
Existence of axially symmetric static solutions of the Einstein-Vlasov system
We prove the existence of static, asymptotically flat non-vacuum spacetimes
with axial symmetry where the matter is modeled as a collisionless gas. The
axially symmetric solutions of the resulting Einstein-Vlasov system are
obtained via the implicit function theorem by perturbing off a suitable
spherically symmetric steady state of the Vlasov-Poisson system.Comment: 32 page
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