5,589 research outputs found
Investigation of the shear-mechanical and dielectric relaxation processes in two mono-alcohols close to the glass transition
Shear-mechanical and dielectric measurements on the two monohydroxy
(mono-alcohol) molecular glass formers 2-ethyl-1-hexanol and 2-butanol close to
the glass transition temperature are presented. The shear-mechanical data are
obtained using the piezoelectric shear-modulus gauge method covering
frequencies from 1mHz to 10kHz. The shear-mechanical relaxation spectra show
two processes, which follow the typical scenario of a structural (alpha)
relaxation and an additional (Johari-Goldstein) beta relaxation. The dielectric
relaxation spectra are dominated by a Debye-type peak with an additional
non-Debye peak visible. This Debye-type relaxation is a common feature peculiar
to mono-alcohols. The time scale of the non-Debye dielectric relaxation process
is shown to correspond to the mechanical structural (alpha) relaxation.
Glass-transition temperatures and fragilities are reported based on the
mechanical alpha relaxation and the dielectric Debye-type process, showing that
the two glass-transition temperatures differ by approximately 10K and that the
fragility based on the Debye-type process is a factor of two smaller than the
structural fragility. If a mechanical signature of the Debye-type relaxation
exists in these liquids, its relaxation strength is at most 1% and 3% of the
full relaxation strength of 2-butanol and 2-ethyl-1-hexanol respectively. These
findings support the notion that it is the non-Debye dielectric relaxation
process that corresponds to the structural alpha relaxation in the liquid.Comment: 8 pages, 6 figures. Minor corrections, updated figures, more
dielectric data show
Photonic crystal fiber with a hybrid honeycomb cladding
We consider an air-silica honeycomb lattice and demonstrate a new approach to
the formation of a core defect. Typically, a high or low-index core is formed
by adding a high-index region or an additional air-hole (or other low-index
material) to the lattice, but here we discuss how a core defect can be formed
by manipulating the cladding region rather than the core region itself.
Germanium-doping of the honeycomb lattice has recently been suggested for the
formation of a photonic band-gap guiding silica-core and here we experimentally
demonstrate how an index-guiding silica-core can be formed by fluorine-doping
of the honeycomb lattice.Comment: 5 pages including 3 figures. Accepted for Optics Expres
Covariant q-differential operators and unitary highest weight representations for U_q su(n,n)
We investigate a one-parameter family of quantum Harish-Chandra modules of
U_q sl(2n). This family is an analog of the holomorphic discrete series of
representations of the group SU(n,n) for the quantum group U_q su(n, n). We
introduce a q-analog of "the wave" operator (a determinant-type differential
operator) and prove certain covariance property of its powers. This result is
applied to the study of some quotients of the above-mentioned quantum
Harish-Chandra modules. We also prove an analog of a known result by J.Faraut
and A.Koranyi on the expansion of reproducing kernels which determines the
analytic continuation of the holomorphic discrete series.Comment: 26 page
Supercooled Liquid Dynamics Studied via Shear-Mechanical Spectroscopy
We report dynamical shear-modulus measurements for five glass-forming liquids
(pentaphenyl trimethyl trisiloxane, diethyl phthalate, dibutyl phthalate,
1,2-propanediol, and m-touluidine). The shear-mechanical spectra are obtained
by the piezoelectric shear-modulus gauge (PSG) method. This technique allows
one to measure the shear modulus ( Pa) of the liquid within a
frequency range from 1 mHz to 10 kHz. We analyze the frequency-dependent
response functions to investigate whether time-temperature superposition (TTS)
is obeyed. We also study the shear-modulus loss-peak position and its
high-frequency part. It has been suggested that when TTS applies, the
high-frequency side of the imaginary part of the dielectric response decreases
like a power law of the frequency with an exponent -1/2. This conjecture is
analyzed on the basis of the shear mechanical data. We find that TTS is obeyed
for pentaphenyl trimethyl trisiloxane and in 1,2-propanediol while in the
remaining liquids evidence of a mechanical process is found. Although
the the high-frequency power law behavior of the shear-loss
may approach a limiting value of when lowering the temperature, we
find that the exponent lies systematically above this value (around 0.4). For
the two liquids without beta relaxation (pentaphenyl trimethyl trisiloxane and
1,2-propanediol) we also test the shoving model prediction, according to which
the the relaxation-time activation energy is proportional to the instantaneous
shear modulus. We find that the data are well described by this model.Comment: 7 pages, 6 figure
Metabolomics-derived marker metabolites to characterize Phaeocystis pouchetii physiology in natural plankton communities
Identical temperature dependence of the time scales of several linear-response functions of two glass-forming liquids
The frequency-dependent dielectric constant, shear and adiabatic bulk moduli,
longitudinal thermal expansion coefficient, and longitudinal specific heat have
been measured for two van der Waals glass-forming liquids,
tetramethyl-tetraphenyl-trisiloxane (DC704) and 5-polyphenyl-4-ether. Within
the experimental uncertainties the loss-peak frequencies of the measured
response functions have identical temperature dependence over a range of
temperatures, for which the Maxwell relaxation time varies more than nine
orders of magnitude. The time scales are ordered from fastest to slowest as
follows: Shear modulus, adiabatic bulk modulus, dielectric constant,
longitudinal thermal expansion coefficient, longitudinal specific heat. The
ordering is discussed in light of the recent conjecture that van der Waals
liquids are strongly correlating, i.e., approximate single-parameter liquids.Comment: 8 pages, 6 figures, Substantially revised versio
Ultra-large bandwidth hollow-core guiding in all-silica Bragg fibers with nano-supports
We demonstrate a new class of hollow-core Bragg fibers that are composed of
concentric cylindrical silica rings separated by nanoscale support bridges. We
theoretically predict and experimentally observe hollow-core confinement over
an octave frequency range. The bandwidth of bandgap guiding in this new class
of Bragg fibers exceeds that of other hollow-core fibers reported in the
literature. With only three rings of silica cladding layers, these Bragg fibers
achieve propagation loss of the order of 1 dB/m.Comment: 9 pages including 5 figure
State business: gender, sex and marriage in Tajikistan
This article examines the relation of the state to masculinity and sexuality by way of an exploration of the sexual problems of a young man and his wife in Tajikistan at the end of the Soviet era. It suggests that the regimeâs inattention to this kind of issue was bound up with the importance to the state of projecting appropriate versions of masculinity. It further posits the idea that the continued refusal of the independent Tajik state to offer appropriate treatments for sexual dysfunction is consistent with the image of modernity President Rahmon wishes to present to the world. The article shows that as masculinity discursively occupies the superior gender position, with men expected to dominate, the state is itself impotent to respond when they are, in fact, unable to do so in sexual practice. However, the myth of male dominance persists to the point that it may prevent women from seeing beyond their subordination and finding mutually beneficial solutions in their familial and sexual relationships
One-year follow-up on liraglutide treatment for prediabetes and overweight/obesity in clozapine- or olanzapine-treated patients
A Micromegas-based low-background x-ray detector coupled to a slumped-glass telescope for axion research
We report on the design, construction and operation of a low background x-ray
detection line composed of a shielded Micromegas (micromesh gaseous structure)
detector of the microbulk technique. The detector is made from radiopure
materials and is placed at the focal point of a ~5 cm diameter, 1.3 m
focal-length, cone-approximation Wolter I x-ray telescope (XRT) comprised of
thermally-formed (or "slumped") glass substrates deposited with multilayer
coatings. The system has been conceived as a technological pathfinder for the
future International Axion Observatory (IAXO), as it combines two of the
techniques (optic and detector) proposed in the conceptual design of the
project. It is innovative for two reasons: it is the first time an x-ray optic
has been designed and fabricated specifically for axion research, and the first
time a Micromegas detector has been operated with an x-ray optic. The line has
been installed at one end of the CERN Axion Solar Telescope (CAST) magnet and
is currently looking for solar axions. The combination of the XRT and
Micromegas detector provides the best signal-to-noise ratio obtained so far by
any detection system of the CAST experiment with a background rate of
5.410counts per hour in the energy region-of-interest and
signal spot area.Comment: 21 pages, 16 figure
- âŠ