1,227 research outputs found
Acrylamide in almond products
Acrylamide was determined in 86 different almond products, such as roasted almonds, almond-containing bakery products, raw almonds, and marzipan. The highest acrylamide concentrations were found in dark roasted almonds, while only moderate acrylamide contents were determined in bakery products. Roasting experiments under different process conditions showed that acrylamide increases with time and that temperature has a much stronger effect on acrylamide formation than time. During roasting reducing sugars are consumed faster and to a larger extent than free asparagine, suggesting that the content of reducing sugars may be a critical factor for acrylamide formation in roasted almonds. Acrylamide was found to decrease in roasted almonds during storage at room temperatur
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Magnetization of polar ice: a measurement of terrestrial dust and extraterrestrial fallout
Laboratory-induced remanent magnetization of polar ice constitutes a measurement of the magnetization carried by the ferromagnetic dust particles in the ice. This non-destructive technique provides a novel kind of information on the dust deposited on the surface of polar ice sheets. Measurements made on ice samples from Greenland (North GRIP ice core) and Antarctica (Vostok and EPICA-Dome C ice cores) allowed the recognition of a fraction of magnetic minerals in ice whose concentration and magnetic properties are directly related to that of insoluble dust. The source of this fraction of magnetic minerals thus appears closely related to terrestrial dust transport and deposition and its magnetic properties are informative of the dust provenance areas. The rock-magnetic properties of the dust may reflect distinct changes of dust source areas from glacial to interglacial periods in agreement with and adding further information to the isotopic (87Sr/86Sr and 143Nd/144Nd) analyses. A second magnetic fraction consists of particles of nanometric size, which are superparamagnetic at freezer temperature and whose concentration is independent of the mass of aerosol dust found in the ice. The source of these nanometric-sized magnetic particles is ascribed to fallout of “meteoric smoke” and their concentration in ice was found to be compatible with the extraterrestrial fallout inferred from Ir concentrations. The diameter of the smoke particles as inferred from magnetic measurements is in the range of about 7–20 nm
Herschel observations of interstellar chloronium
Using the Herschel Space Observatory's Heterodyne Instrument for the
Far-Infrared (HIFI), we have observed para-chloronium (H2Cl+) toward six
sources in the Galaxy. We detected interstellar chloronium absorption in
foreground molecular clouds along the sight-lines to the bright submillimeter
continuum sources Sgr A (+50 km/s cloud) and W31C. Both the para-H2-35Cl+ and
para-H2-37Cl+ isotopologues were detected, through observations of their
1(11)-0(00) transitions at rest frequencies of 485.42 and 484.23 GHz,
respectively. For an assumed ortho-to-para ratio of 3, the observed optical
depths imply that chloronium accounts for ~ 4 - 12% of chlorine nuclei in the
gas phase. We detected interstellar chloronium emission from two sources in the
Orion Molecular Cloud 1: the Orion Bar photodissociation region and the Orion
South condensation. For an assumed ortho-to-para ratio of 3 for chloronium, the
observed emission line fluxes imply total beam-averaged column densities of ~
2.0E+13 cm-2 and ~ 1.2E+13 cm-2, respectively, for chloronium in these two
sources. We obtained upper limits on the para-H2-35Cl+ line strengths toward H2
Peak 1 in the Orion Molecular cloud and toward the massive young star AFGL
2591. The chloronium abundances inferred in this study are typically at least a
factor ~10 larger than the predictions of steady-state theoretical models for
the chemistry of interstellar molecules containing chlorine. Several
explanations for this discrepancy were investigated, but none has proven
satisfactory, and thus the large observed abundances of chloronium remain
puzzling.Comment: Accepted for publication in the Astrophysical Journa
Proving knowledge of isogenies – A survey
Isogeny-based cryptography is an active area of research in post-quantum public key cryptography. The problem of proving knowledge of an isogeny is a natural problem that has several applications in isogeny-based cryptography, such as allowing users to demonstrate that they are behaving honestly in a protocol. It is also related to isogeny-based digital signatures. Over the last few years, there have been a number of advances in this area, but there are still many open problems. This paper aims to give an overview of the topic and highlight some open problems and directions for future research
Effect of Partial Crystallization on the Structural and Luminescence Properties of Er3+-Doped Phosphate Glasses
Er-doped phosphate glass ceramics were fabricated by melt-quenching technique followed by a heat treatment. The effect of the crystallization on the structural and luminescence properties of phosphate glasses containing Al2O3, TiO2, and ZnO was investigated. Themorphological and structural properties of the glass ceramics were characterized by Field Emission-Scanning Electron Microscopy (FE-SEM), X-ray Diffraction (XRD), and micro-Raman spectroscopy. Additionally, the luminescence spectra and the lifetime values were measured in order to study the influence of the crystallization on the spectroscopic properties of the glasses. The volume ratio between the crystal and the glassy phases increased along with the duration of the heat treatment. The crystallization of the glass ceramics was confirmed by the presence of sharp peaks in the XRD patterns and different crystal phases were
identified depending on the glass composition. Sr(PO3)2 crystals were found to precipitate in all the
investigated glasses. As evidenced by the spectroscopic properties, the site of the Er3+ ions was not
strongly affected by the heat treatment except for the fully crystallized glass ceramic which does not
contain Al2O3, TiO2, and ZnO. An increase of the lifetime was also observed after the heat treatment
of this glass. Therefore, we suspect that the Er3+ ions are incorporated in the precipitated crystals
only in this glass ceramic
Molecular absorption lines toward star-forming regions : a comparative study of HCO+, HNC, HCN, and CN
Aims. The comparative study of several molecular species at the origin of the
gas phase chemistry in the diffuse interstellar medium (ISM) is a key input in
unraveling the coupled chemical and dynamical evolution of the ISM. Methods.
The lowest rotational lines of HCO+, HCN, HNC, and CN were observed at the
IRAM-30m telescope in absorption against the \lambda 3 mm and \lambda 1.3 mm
continuum emission of massive star-forming regions in the Galactic plane. The
absorption lines probe the gas over kiloparsecs along these lines of sight. The
excitation temperatures of HCO+ are inferred from the comparison of the
absorptions in the two lowest transitions. The spectra of all molecular species
on the same line of sight are decomposed into Gaussian velocity components.
Most appear in all the spectra of a given line of sight. For each component, we
derived the central opacity, the velocity dispersion, and computed the
molecular column density. We compared our results to the predictions of
UV-dominated chemical models of photodissociation regions (PDR models) and to
those of non-equilibrium models in which the chemistry is driven by the
dissipation of turbulent energy (TDR models). Results. The molecular column
densities of all the velocity components span up to two orders of magnitude.
Those of CN, HCN, and HNC are linearly correlated with each other with mean
ratios N(HCN)/N(HNC) = 4.8 1.3 and N(CN)/N(HNC) = 34 12, and more
loosely correlated with those of HCO+, N(HNC)/N(HCO+) = 0.5 0.3,
N(HCN)/N(HCO+) = 1.9 0.9, and N(CN)/N(HCO+) = 18 9. These ratios
are similar to those inferred from observations of high Galactic latitude lines
of sight, suggesting that the gas sampled by absorption lines in the Galactic
plane has the same chemical properties as that in the Solar neighbourhood. The
FWHM of the Gaussian velocity components span the range 0.3 to 3 km s-1 and
those of the HCO+ lines are found to be 30% broader than those of CN-bearing
molecules. The PDR models fail to reproduce simultaneously the observed
abundances of the CN-bearing species and HCO+, even for high-density material
(100 cm-3 < nH < 104 cm-3). The TDR models, in turn, are able to reproduce the
observed abundances and abundance ratios of all the analysed molecules for the
moderate gas densities (30 cm-3 < nH < 200 cm-3) and the turbulent energy
observed in the diffuse interstellar medium. Conclusions. Intermittent
turbulent dissipation appears to be a promising driver of the gas phase
chemistry of the diffuse and translucent gas throughout the Galaxy. The details
of the dissipation mechanisms still need to be investigated
Herschel/HIFI observations of interstellar OH+ and H2O+ towards W49N: a probe of diffuse clouds with a small molecular fraction
We report the detection of absorption by interstellar hydroxyl cations and
water cations, along the sight-line to the bright continuum source W49N. We
have used Herschel's HIFI instrument, in dual beam switch mode, to observe the
972 GHz N = 1 - 0 transition of OH+ and the 1115 GHz 1(11) - 0(00) transition
of ortho-H2O+. The resultant spectra show absorption by ortho-H2O+, and strong
absorption by OH+, in foreground material at velocities in the range 0 to 70
km/s with respect to the local standard of rest. The inferred OH+/H2O+
abundance ratio ranges from ~ 3 to ~ 15, implying that the observed OH+ arises
in clouds of small molecular fraction, in the 2 - 8% range. This conclusion is
confirmed by the distribution of OH+ and H2O+ in Doppler velocity space, which
is similar to that of atomic hydrogen, as observed by means of 21 cm absorption
measurements, and dissimilar from that typical of other molecular tracers. The
observed OH+/H abundance ratio of a few E-8 suggests a cosmic ray ionization
rate for atomic hydrogen of (0.6 - 2.4) E-16 s-1, in good agreement with
estimates inferred previously for diffuse clouds in the Galactic disk from
observations of interstellar H3+ and other species.Comment: Accepted for publication in A&A Letter
Strategic Location Choice Under Dynamic Oligopolistic Competition and Spillovers
Colombo L, Dawid H. Strategic Location Choice Under Dynamic Oligopolistic Competition and Spillovers. Journal of Economic Dynamics and Control. 2014;48:288-307.This paper investigates firms’ optimal location choices explicitly accounting for the role of inwards and outwards knowledge spillovers in a dynamic Cournot oligopoly with firms that are heterogeneous in their ability to carry out cost-reducing R&D. Firms can either locate in an industrial cluster or in isolation. Technological spillovers are exchanged between the firms in the cluster. It is shown that a technological leader has an incentive to locate in isolation only if her advantage exceeds a certain threshold, which is increasing in firms’ discount rate, in industry dispersion, and in the intensity of knowledge spillovers. Scenarios are identified where although it is optimal for the technological leader to locate in isolation, from a welfare perspective it would be desirable that she locates in the cluster
Comparative study of CH+ and SH+ absorption lines observed towards distant star-forming regions
Aims. The HIFI instrument onboard Herschel has allowed high spectral
resolution and sensitive observations of ground-state transi- tions of three
molecular ions: the methylidyne cation CH+, its isotopologue 13CH+, and
sulfanylium SH+. Because of their unique chemical properties, a comparative
analysis of these cations provides essential clues to the link between the
chemistry and dynamics of the diffuse interstellar medium. Methods. The CH+,
13CH+, and SH+ lines are observed in absorption towards the distant high-mass
star-forming regions (SFRs) DR21(OH), G34.3+0.1, W31C, W33A, W49N, and W51, and
towards two sources close to the Galactic centre, SgrB2(N) and SgrA*+50. All
sight lines sample the diffuse interstellar matter along pathlengths of several
kiloparsecs across the Galactic Plane. In order to compare the velocity
structure of each species, the observed line profiles were deconvolved from the
hyperfine structure of the SH+ transition and the CH+, 13CH+, and SH+ spectra
were independently decomposed into Gaussian velocity components. To analyse the
chemical composition of the foreground gas, all spectra were divided, in a
second step, into velocity intervals over which the CH+, 13CH+, and SH+ column
densities and abundances were derived. Results. SH+ is detected along all
observed lines of sight, with a velocity structure close to that of CH+ and
13CH+. The linewidth distributions of the CH+, SH+, and 13CH+ Gaussian
components are found to be similar. These distributions have the same mean
( ~ 4.2 km s-1) and standard deviation
(\sigma(\delta\u{psion}) ~ 1.5 km s-1). This mean value is also close to that
of the linewidth distribution of the CH+ visible transitions detected in the
solar neighbourhood. We show that the lack of absorption components narrower
than 2 km s-1 is not an artefact caused by noise: the CH+, 13CH+, and SH+ line
profiles are therefore statistically broader than those of most species
detected in absorption in diffuse interstellar gas (e. g. HCO+, CH, or CN). The
SH+/CH+ column density ratio observed in the components located away from the
Galactic centre spans two orders of magnitude and correlates with the CH+
abundance. Conversely, the ratio observed in the components close to the
Galactic centre varies over less than one order of magnitude with no apparent
correlation with the CH+ abundance. The observed dynamical and chemical
properties of SH+ and CH+ are proposed to trace the ubiquitous process of
turbulent dissipation, in shocks or shears, in the diffuse ISM and the specific
environment of the Galactic centre regions
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