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At least 325 records · Page 18Linked to original sources
PubMed2003

Biological dosimetry of complex ion radiation fields.

We report on a set of cell survival experiments performed in complex field combinations of therapeutic 12C ion beams. CHO cells were exposed to the superposition of two or three fields of 12C ions arranged in a similar way to real patient treatments. Two-dimensional survival distributions were measured and compared with the predictions of the TRiP98 treatment planning system. Good agreement was found in general. In particular the method of tissue sparing using dose ramps could be verified.

Animals↗
PubMed2003

Double photoexcitation of helium in a strong dc electric field.

We report the first experimental measurements of the effect of an applied field on the photoexcitation and autoionization of doubly excited states of helium. Ground-state photoionization spectra have been measured in the region below the He+(N=2) threshold with static electric fields of up to 84.4 kV/cm across the interaction region. The results are compared to the theoretical calculations of Chung et al. [J. Phys. B 34, 165 (2001)]], which are the only calculations available in this regime. Transitions to several states in the N=2, n=6 manifold are assigned, and a wealth of new structure is observed. Our data show that many more series are mixed in by the field than those predicted by theory.

Journal Article↗
PubMed2004

Polarization spectroscopy of gaseous tropolone in a strong electric field.

We report studies of polarization spectroscopy of gaseous tropolone in a strong electric field using resonantly enhanced multiphoton ionization. The electric field induces localization of the tunneling proton between the two equivalent oxygen atoms. As a result, the C2v symmetry of the molecular frame is broken, and the parity selection rule is violated. The field induced transitions are type A with transition dipoles perpendicular to those under field free conditions. The polarization ratios, i.e., the ratios of the overall excitation yield under different polarizations of the resonant laser, thus deviate from those of a pure type B transition. In a field of 60 kV/cm, the experimental polarization ratio implies an essentially equal mixture of type B and type A transitions. Moreover, the induced transitions overlap with the two field-free subbands, and the resulting intensity ratios between the two subbands demonstrate dependence on the applied electric field. These observations can be qualitatively modeled using a quantum mechanical approach by assuming a two level system. A puzzling result is the magnitude of the transition dipole of the induced transition, which is proven to be essentially linearly dependent on the applied electric field.

Journal Article↗
PubMed2002

Two-stage Kondo effect in a quantum dot at a high magnetic field.

We report a strong Kondo effect (Kondo temperature approximately 4 K) at high magnetic field in a selective area growth semiconductor quantum dot. The Kondo effect is ascribed to a singlet-triplet transition in the ground state of the dot. At the transition, the low-temperature conductance approaches the unitary limit. Away from the transition, for low bias voltages and temperatures, the conductance is sharply reduced. The observed behavior is compared to predictions for a two-stage Kondo effect in quantum dots coupled to single-channel leads.

Journal Article↗
PubMed2004

Interaction of separated ferromagnetic domains in a hole-doped manganite achieved by a magnetic field.

We report the change in the magnetic microstructure with the application of a magnetic field to a hole-doped manganite La0.81Sr0.19MnO3 in the mixed-phase state, in which ferromagnetic and paramagnetic phases coexist. In situ observations by electron holography have revealed that the applied magnetic field generates a "channel" of the magnetic flux in the paramagnetic phase region, thereby connecting the separated ferromagnetic domains. The magnetic flux density of this channel is estimated at 0.33 T, which is comparable with that of the ferromagnetic domains. The connection of the separated ferromagnetic domains appears to promote the conduction in the mixed-phase state as predicted for many manganites exhibiting the magnetoresistance effect.

Journal Article↗
PubMed2003

[Mycoplasma synoviae-associated amyloid arthropathy in white leghorns: case report].

Under field circumstances amyloid arthropathy was nerve recorded in white layers, while experimentally their brown counterparts were found to be more susceptible to the induction of amyloid arthropathy, although articular amyloid was found in a few white leghorns. In the present manuscript the first field case of amyloid arthropathy in white layers associated with Mycoplasma synoviae is reported. In the same house where the white birds were housed, brown layers were present. The condition was much more severe in the latter chickens. The different susceptibility between both breeds is discussed in view of previously performed research.

Amyloidosis↗
PubMed1989

Two rare developmental defects of the lower limbs with confirmation of the Lewin and Opitz hypothesis on the fibular and tibial developmental fields.

We report on two unrelated patients with malformations of the lower limbs. One had a unilateral apparent doubling of the volume of the femur with distal bifurcation, shortness of the tibiae, absence of fibulae, and lateral ray deficiencies of both feet. The other had a partial duplication of the distal left femur, hypoplasia and proximal dislocation of the ipsilateral tibia, syndactyly of the right 1st and 2nd toes, and preaxial polydactyly of the left foot. This report supports the hypothesis of Lewin and Opitz on the presence of two distinct fields of development: the fibular and the tibial.

Abnormalities, Multiple↗
PubMed1965

EVALUATION OF TYPHOID VACCINES IN THE LABORATORY AND IN A CONTROLLED FIELD TRIAL IN POLAND. PRELIMINARY REPORT.

In 1961 a controlled field trial of anti-typhoid vaccines was carried out in 25 regions in Poland. Four types of vaccine were studied: (1) bacterial acetone-killed and -dried vaccine (two kinds), (2) bacterial formol-killed phenol-preserved vaccine, (3) Westphal's endotoxin adsorbed on aluminium hydroxide, and (4) Grasset's vaccine (autolysate of typhoid bacilli adsorbed on aluminium hydroxide). The control vaccine was tetanus toxoid. A total of 690 655 persons received two inoculations. Prior to the field trial, laboratory tests were carried out on the vaccines, postvaccinal reactions were studied, and a serological examination was made of randomly selected blood samples. The vaccination was followed by a two-year survey of cases of typhoid and other diseases. Among children aged 5-14 years, the formol-killed phenol-preserved vaccine was found to be the most effective and Grasset's vaccine the least. Among adults aged 15-60 years, no conclusive evidence for the effectiveness of the vaccines could be obtained owing to the small number of cases. This may be due to the maintenance of immunity through repeated annual vaccination with bacterial vaccines.

Adolescent↗
PubMed1993

Altered protein synthesis in a cell-free system exposed to a sinusoidal magnetic field.

This report describes a new approach for examining weak extremely low frequency (ELF) electric and magnetic field interactions with living systems that exploits a cell-free transcription/translation system derived from Escherichia coli. Using two-dimensional polyacrylamide gel electrophoresis we previously had determined that the level of the alpha subunit of RNA polymerase in intact E. coli was elevated by exposure to weak ELF magnetic fields. In this paper, plasmids containing the alpha, or both the beta,beta' subunits of the RNA polymerase from E. coli were placed into a cell-free expression system. When this transcription/translation system was exposed to a 72-Hz sinusoidal magnetic field in the range 0.07 to 1.1 mT (rms) for periods of 5 min to 1 h, expression was enhanced. Weaker fields must be applied longer to produce an effect. For 10 min of field exposure, the threshold for an effect is 0.1 mT. These experiments demonstrate that an intact membrane is not an absolute requirement for transducing magnetic bio-effects.

Cell-Free System↗
PubMed2000

Structure and dynamics of magnetorheological fluids in rotating magnetic fields

We report on the orientation dynamics and aggregation processes of magnetorheological fluids subject to rotating magnetic fields using the technique of scattering dichroism. In the presence of stationary fields we find that the mean length of the field-induced aggregates reaches a saturation value due to finite-size effects. When a rotating field is imposed, we see the chains rotate with the magnetic field frequency (synchronous regime) but with a retarded phase angle for all the rotational frequencies applied. However, two different behaviors are found below or above a critical frequency f(c). Within the first regime (low frequency values) the size of the aggregates remains almost constant, while at high frequencies this size becomes shorter due to hydrodynamic drag. Experimental results have been reproduced by a simple model considering a torque balance on the chainlike aggregates.

Journal Article↗
PubMed2003

New electro-optic effect: sum-frequency generation from optically active liquids in the presence of a dc electric field.

We report the observation of sum-frequency signals that depend linearly on an applied electrostatic field and that change sign with the handedness of an optically active solute. This recently predicted chiral electro-optic effect exists in the electric-dipole approximation. The static electric field gives rise to an electric-field-induced sum-frequency signal (an achiral third-order process) that interferes with the chirality-specific sum-frequency at second order. The cross-terms linear in the electrostatic field constitute the effect and may be used to determine the absolute sign of second- and third-order nonlinear-optical susceptibilities in isotropic media.

Electromagnetic Fields↗
PubMed2001

Optical phase contrast measurement of ultrasonic fields.

This report describes an optical phase contrast imaging technique for the measurement of wide bandwidth ultrasound fields in water. In this method, a collimated optical wavefront (lambda(l) = 810 nm) impinges on a wide bandwidth ultrasound pulse. The method requires that refractive index perturbations induced by the ultrasound field be sufficiently small. Specifically, on exit from the acoustic field, the phase of the optical wavefront must be proportional to the ray sum of local density taken in the direction of propagation of the incident optical wave. A similar restriction is placed on the dimensions of the ultrasound pulse. Repeated measurement of this phase as the ultrasound field is rotated through 180 degrees about an axis normal to the direction of propagation of the incident optical wave generates the Radon transform of the ultrasonically induced refractive index perturbation. Standard tomographic reconstruction techniques are used to reconstruct the full three-dimensional refractive index perturbation. A simple two-lens imaging system and an optical signal processing element from phase contrast microscopy provide a method of directly measuring an affine function of the desired optical phase for small optical phase shifts. The piezo- and elasto-optic coefficients (the first partial derivatives of refractive index with respect to density and pressure) relate refractive index to density and pressure via a linear model. The optical measurement method described in this paper provides a direct, quantitative measurement of the piezo- and elasto-optic coefficients (from the density or pressure fields).

Journal Article↗
PubMed2005

CIDEP of micellized radical pairs in low magnetic fields.

We report the first experimental study of chemically induced electron spin polarization (CIDEP) processes in low magnetic fields for spin-correlated radical pairs (SCRPs) in micellar environments. Photoexcitation of (2,4,6-trimethylbenzoyl) diphenylphosphine oxide (TMBDPO) leads to the radical pair comprised of acyl radical 1 and phosphonyl radical 2. The spin polarization, which is very strong in free solution even at zero field, was detected using L-band time-resolved electron paramagnetic resonance (TREPR) spectroscopy with specially modified resonators. The mechanism of formation and decay of low field CIDEP in SCRPs is presented and discussed. The prominent difference between low and high field spectra in micelles is the absence of anti-phase structure for radical 2 with HFI a > B0. This feature is consistent with the proposed polarization mechanism and theoretical predictions.

Electron Spin Resonance Spectroscopy↗
PubMed2006

Multiparadigm modeling of dynamical crack propagation in silicon using a reactive force field.

We report a study of dynamic cracking in a silicon single crystal in which the ReaxFF reactive force field is used for several thousand atoms near the crack tip, while more than 100,000 atoms are described with a nonreactive force field. ReaxFF is completely derived from quantum mechanical calculations of simple silicon systems without any empirical parameters. Our results reproduce experimental observations of fracture in silicon including changes in crack dynamics for different crack orientations.

Journal Article↗
PubMed2000

Assessing impaired hypoglycemia awareness in type 1 diabetes: agreement of self-report but not of field study data with the autonomic symptom threshold during experimental hypoglycemia.

OBJECTIVE: The aim of our study was to determine the agreement of two noninvasive methods, a self-report and a field study method, for the assessment of impaired hypoglycemia awareness with a gold standard criterion of hypoglycemia awareness, the autonomic symptom threshold during experimental hypoglycemia. RESEARCH DESIGN AND METHODS: A total of 19 type 1 diabetic patients completed a standardized questionnaire to assess impaired hypoglycemia awareness and performed a hand-held computer (HHC) study to assess their recognition of hypoglycemic episodes occurring during 24 weeks. Patients subsequently underwent a stepped hypoglycemic clamp to study responses to standardized hypoglycemia. Diagnoses of impaired hypoglycemia awareness were based on the separate self-report questions, a composite self-report score, and three different cutoff levels for the percentage of accurately recognized hypoglycemic episodes during the field study Agreement of these noninvasive measures with the hypoglycemic clamp measure were tested by calculating kappa values, sensitivity, and specificity. RESULTS: The composite self-report score agreed reasonably well with the hypoglycemic clamp measure (kappa 0.49, sensitivity 66.7%, and specificity 85.7%) and showed a better agreement than the separate self-report questions. The HHC criterion of impaired hypoglycemia awareness did not agree with the hypoglycemic clamp criterion at any of the cutoff levels tested. CONCLUSIONS: The composite self-report tested in this study is a reasonably reliable assessment method for the diagnosis of impaired hypoglycemia awareness, using the physiological definition of an absence of autonomic symptoms at a blood glucose level of 3 mmol/l. In contrast, the recognition of hypoglycemic events in everyday life as measured using the HHC method is not related to the hypoglycemic clamp criterion.

Adult↗
PubMed1984

Use of pulsed electromagnetic fields in Perthes disease: report of a pilot study.

A pilot study of pulsed electromagnetic fields (PEMFs) in the treatment of 10 older children with unilateral Perthes disease of the hip is reported. Patients were allowed to walk using crutches, with the affected hip splinted by the Birmingham containment orthosis during the day. For 10 h during the night the affected hip was exposed to PEMFs delivered via a pair of coils, mounted anterior and posterior to the hip joint on a plastic abduction orthosis. Splintage time of this group was compared with that of 72 patients selected at random from a historical control group of 200 patients. The 72 patients and the 10 children were assigned to early or late groups depending on the radiologic evolution of the disease when treatment commenced. The group of 10 children showed an overall reduction of time in all splintage of 32% in early cases (to 12.8 months) and 18% in late cases (to 13.5 months). No untoward effects were detected during the 2 years that these children have been under observation. In view of the apparent safety of PEMFs and their effects in this limited population of older patients with advanced Perthes disease, a double-blind study in younger patients with earlier lesions seems to be justified.

Child↗
PubMed1989

Judging the reflection of misoriented patterns in the right and left visual fields.

The reported study demonstrates that performance asymmetries between normal or reflected letters presented in the right and left visual field favors the right visual field when stimulus patterns are blocked and rotated 90 degrees clockwise and favors the left visual field when they are blocked and rotated 90 degrees counterclockwise. When stimuli are rotated, the orientations of the patterns define a coordinate system that is independent of upright. It is suggested that our results are due to subjects sampling the different areas in the visual field relative to this coordinate system. The right visual field was given priority when the patterns were oriented so their "tops" were pointing rightward and the left visual field was given priority when the patterns were oriented so their tops were pointing leftward. Neither differences in the stimulus image on the retina in the two rotated conditions, eye movements, nor direct access to one hemisphere or the other could account for these effects.

Adult↗