54 research outputs found
On the Nature of the Debye-Process in Monohydroxy Alcohols: 5-Methyl-2-Hexanol Investigated by Depolarized Light Scattering and Dielectric Spectroscopy
The slow Debye-like relaxation in the dielectric spectra of monohydroxy
alcohols is a matter of long standing debate. In the present work, we probe
reorientational dynamics of 5-methyl-2-hexanol with dielectric spectroscopy and
depolarized light scattering (DDLS) in the supercooled regime. While in a
previous study of a primary alcohol no indication of the Debye peak in the DDLS
spectra was found, we now for the first time report clear evidence of a Debye
contribution in a monoalcohol in DDLS. A quantitative comparison between the
dielectric and DDLS manifestation of the Debye peak reveals that while the
dielectric Debye process represents fluctuations in the end-to-end vector
dipole moment of the transient chains, its occurrence in DDLS shows a more
local signature and is related to residual correlations which occur due to a
slight anisotropy of the -relaxation caused by the chain formation.Comment: 5 pages, 5 figures; accepted in Phys. Rev. Let
Dipole-dipole correlations and the Debye process in the dielectric response of non-associating glass forming liquids
The non-exponential shape of the -process observed in supercooled
liquids is considered as one of the hallmarks of glassy dynamics and has thus
been under study for decades, but is still poorly understood. For a polar van
der Waals liquid, we show here - in line with a recent theory - that
dipole-dipole correlations give rise to an additional process in the dielectric
spectrum slightly slower than the -relaxation, which renders the
resulting combined peak narrower than observed by other experimental
techniques. This is reminiscent of the Debye process found in monohydroxy
alcohols. The additional peak can be suppressed by weakening the dipole-dipole
interaction via dilution with a nonpolar solvent
Bestockung und Beschattung : Erfassung an Fliessgewässern
Uferbestockungen haben neben der wichtigen Funktion der Beschattung und Abkühlung der Gewässer noch zahlreiche weitere wertvolle Funktionen. Eine schweizweite Bestandesübersicht der Bestockung bzw. Beschattung entlang der Bäche und Flüsse besteht derzeit noch nicht. Diese Informationslücke soll zukünftig mit geeigneten Methoden geschlossen werden
Impairment in predictive processes during auditory mismatch negativity in ScZ: evidence from event-related fields
Patients with schizophrenia (ScZ) show pronounced dysfunctions in auditory perception but the underlying mechanisms as well as the localization of the deficit remain unclear. To examine these questions, the current study examined whether alterations in the neuromagnetic mismatch negativity (MMNm) in ScZ-patients could involve an impairment in sensory predictions in local sensory and higher auditory areas. Using a whole-head MEG-approach, we investigated the MMNm as well as P300m and N100m amplitudes during a hierarchical auditory novelty paradigm in 16 medicated ScZ-patients and 16 controls. In addition, responses to omitted sounds were investigated, allowing for a critical test of the predictive coding hypothesis. Source-localization was performed to identify the generators of the MMNm, omission responses as well as the P300m. Clinical symptoms were examined with the positive and negative syndrome scale. Event-related fields (ERFs) to standard sounds were intact in ScZ-patients. However, the ScZ-group showed a reduction in the amplitude of the MMNm during both local (within trials) and global (across trials) conditions as well as an absent P300m at the global level. Importantly, responses to sound omissions were reduced in ScZ-patients which overlapped both in latency and generators with the MMNm sources. Thus, our data suggest that auditory dysfunctions in ScZ involve impaired predictive processes that involve deficits in both automatic and conscious detection of auditory regularities
Temperature dependence of the static permittivity andintegral formula for the Kirkwood correlation factor ofsimple polar fluids
An exact integral formula for the Kirkwood correlation factor of isotropic
polar fluids is derived from the equilibrium averaged rotational Dean
equation, which as compared to previous approaches easily lends itself to
further approximations. The static linear permittivity of polar fluids
is calculated as a function of temperature, density and molecular
dipole moment in vacuo for arbitrary pair interaction potentials. Then, using
the Kirkwood superposition approximation for the three-body orientational
distribution function, we suggest a simple way to construct model potentials of
mean torques considering permanent and induced dipole moments. We successfully
compare the theory with the experimental temperature dependence of the static
linear permittivity of various polar fluids such as a series of linear
monohydroxy alcohols, water, tributyl phosphate, acetonitrile, acetone,
nitrobenzene and dimethyl sulfoxide, by fitting only one single parameter,
which describes the induction to dipole-dipole energy strength ratio. We
demonstrate that comparing the value of with unity in order to deduce the
alignment state of permanent dipole pairs, as is currently done is in many
situations, is a misleading oversimplification, while the correct alignment
state is revealed when considering the proper interaction potential. Moreover
we show, that picturing H-bonding polar fluids as polar molecules with
permanent and induced dipole moments without invoking any specific H-bonding
mechanism is in many cases sufficient to explain experimental data of the
static dielectric constant. In this light, the failure of the theory to
describe the experimental temperature dependence of the static dielectric
constant of glycerol, a non-rigid polyalcohol, is not due to the lack of
specific H-bonding mechanisms, but rather to an oversimplified model potential
for that particular molecule
Universal Structural Relaxation in Supercooled Liquids
One of the hallmarks of molecular dynamics in deeply supercooled liquids is
the non-exponential character of the relaxation functions. It has been a long
standing issue if 'universal' features govern the lineshape of glassy dynamics
independent of any particular molecular structure or interaction. In the paper,
we elucidate this matter by giving a comprehensive comparison of the spectral
shape of depolarized light scattering and dielectric data of deeply supercooled
liquids. The light scattering spectra of very different systems, e.g. hydrogen
bonding and van der Waals liquids but also ionic systems, almost perfectly
superimpose and show a generic lineshape of the structural relaxation,
approximately following a high frequency power law . However,
the dielectric loss peak shows a more individual shape. In systems with low
dipole moment generic behavior is also observed in the dielectric spectra,
while in strongly dipolar liquids additional crosscorrelation contributions
mask the generic structural relaxation
Acute Motor Axonal Neuropathy in a Patient with Metastatic Pancreatic Neuroendocrine Tumor Receiving Chemotherapy with Capecitabine and Temozolomide: A Case Report
We report a case of a 37- year old female patient with metastatic pancreatic neuroendocrine tumor that developed acute motor axonal neuropathy after receiving chemotherapy with capecitabine and temozolomide. She had repeatedly progressed after several surgical resections of her liver metastases, other hepatic directed procedures, several sessions of peptide receptor radionuclide therapy and two systemic treatment lines. When we started a third line therapy with capecitabine (1500 mg absolute twice daily, day 1-14) and temozolomide (360 mg absolute in two divided doses on day 1-5) in a 28 days long cycle, she unexpectedly developed a progressive weakness of the upper and lower limbs and dysphagia. The diagnosis of acute motor axonal neuropathy was confirmed by nerve conduction studies. The patient`s condition improved rapidly after chemotherapy was stopped and plasma exchange (nine sessions) as well as a maintenance therapy with intravenous immunoglobulins was started. She was almost asymptomatic seven months after onset of symptoms. This case describes a previously unreported association between acute motor axonal neuropathy and chemotherapy with capecitabine and temozolomide
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