402 research outputs found
Assessing habitat-suitability models with a virtual species
This paper compares two habitat-suitability assessing methods, the Ecological Niche Factor Analysis (ENFA) and the Generalised Linear Model (GLM), to see how well they cope with three different scenarios. The main difference between these two analyses is that GLM is based on species presence/absence data while ENFA on presence data only. A virtual species was created and then dispatched in a GIS-model of a real landscape following three historic scenarios: 1° spreading, 2° at equilibrium and 3° overabundant species. In each situation, the virtual species was sampled and these simulated data sets were used as input for the ENFA and GLM to reconstruct the habitat suitability model. The results showed that ENFA is very robust to the quality and quantity of the data, giving good results in the three scenarios. GLM was badly affected in the case of the spreading species but produced slightly better results than ENFA when the species was overabundant; at equilibrium, both methods produced equivalent results. The use of a virtual species proved to be a very efficient method, allowing to fully control the quality of the input data as well as to accurately evaluate the predictive power of both analyses
MA
thesisThe purpose of this work is to analyze Como agua para chocolate, a contemporary work by the Mexican writer Laura Esquivel. Reading this novel, I was impressed with the description of food which permeates throughout the conceptualization of this literary narration. The symbolism of edibles and the profound impact of their effect invade the dynamics connecting the individual, society, and woman as a single identity. This thesis attemps to show the development of the culinary theme as a tool. Esquivel utilizes it to cope with a level that surpassess the common, every day survival and thereby penetrates the socio-individual-cultural stratum that is intricately developed. The Nutrition;al symbolism, the Mexican Revolution, the love, the hate, the memories, the infancy, the passion, and other issues, form a conglomérate of actions and make us confront an analytical world with psyco-sociological depth. The dismemberment of the Mexican woman that Esquivel presents is a challenge to my own Latin-American heritage. The structure of Chocolate will be defined as a socio-individual rebellion presenting the idiosyncracies of a period that explains the present
Studies on the metabolism and toxicological detection of the new psychoactive designer drug 2-(4-iodo-2,5-dimethoxyphenyl)-N-[(2-methoxyphenyl)methyl]ethanamine (25I-NBOMe) in human and rat urine using GC-MS, LC-MSn, and LC-HR-MS/MS
25I-NBOMe, a new psychoactive substance, is a potent 5-HT2A receptor agonist with strong hallucinogenic potential. Recently, it was involved in several fatal and non-fatal intoxication cases. The aim of the present work was to study its phase I and II metabolism and its detectability in urine screening approaches. After application of 25I-NBOMe to male Wistar rats, urine was collected over 24 h. The phase I and II metabolites were identified by LC-HR-MS/MS in urine after suitable workup. For the detectability studies, standard urine screening approaches (SUSA) by GC-MS, LC-MSn, and LC-HR-MS/MS were applied to rat and also to authentic human urine samples submitted for toxicological analysis. Finally, an initial CYP activity screening was performed to identify CYP isoenzymes involved in the major metabolic steps. 25I-NBOMe was mainly metabolized by O-demethylation, O,O-bis-demethylation, hydroxylation, and combinations of these reactions as well as by glucuronidation and sulfation of the main phase I metabolites. All in all, 68 metabolites could be identified. Intake of 25I-NBOMe was detectable mainly via its metabolites by both LC-MS approaches, but not by the GC-MS SUSA. Initial CYP activity screening revealed the involvement of CYP1A2 and CYP3A4 in hydroxylation and CYP2C9 and CYP2C19 in O-demethylation. The presented study demonstrated that 25I-NBOMe was extensively metabolized and could be detected only by the LC-MS screening approaches. Since CYP2C9 and CYP3A4 are involved in initial metabolic steps, drug–drug interactions might occur in certain constellations
Functional Evolution of Free Quantum Fields
We consider the problem of evolving a quantum field between any two (in
general, curved) Cauchy surfaces. Classically, this dynamical evolution is
represented by a canonical transformation on the phase space for the field
theory. We show that this canonical transformation cannot, in general, be
unitarily implemented on the Fock space for free quantum fields on flat
spacetimes of dimension greater than 2. We do this by considering time
evolution of a free Klein-Gordon field on a flat spacetime (with toroidal
Cauchy surfaces) starting from a flat initial surface and ending on a generic
final surface. The associated Bogolubov transformation is computed; it does not
correspond to a unitary transformation on the Fock space. This means that
functional evolution of the quantum state as originally envisioned by Tomonaga,
Schwinger, and Dirac is not a viable concept. Nevertheless, we demonstrate that
functional evolution of the quantum state can be satisfactorily described using
the formalism of algebraic quantum field theory. We discuss possible
implications of our results for canonical quantum gravity.Comment: 21 pages, RevTeX, minor improvements in exposition, to appear in
Classical and Quantum Gravit
An SU(2) Analog of the Azbel--Hofstadter Hamiltonian
Motivated by recent findings due to Wiegmann and Zabrodin, Faddeev and
Kashaev concerning the appearence of the quantum U_q(sl(2)) symmetry in the
problem of a Bloch electron on a two-dimensional magnetic lattice, we introduce
a modification of the tight binding Azbel--Hofstadter Hamiltonian that is a
specific spin-S Euler top and can be considered as its ``classical'' analog.
The eigenvalue problem for the proposed model, in the coherent state
representation, is described by the S-gap Lam\'e equation and, thus, is
completely solvable. We observe a striking similarity between the shapes of the
spectra of the two models for various values of the spin S.Comment: 19 pages, LaTeX, 4 PostScript figures. Relation between Cartan and
Cartesian deformation of SU(2) and numerical results added. Final version as
will appear in J. Phys. A: Math. Ge
Molecular clouds in the center of M81
We investigate the molecular gas content and the excitation and fragmentation
properties in the central region of the spiral galaxy Messier 81 in both the
^{12}CO(1-0) and ^{12}CO(2-1) transitions. We have recently observed the two
transitions of CO in the M~81 center with A, B, and HERA receivers of the IRAM
30-m telescope. We find no CO emission in the inner 300 pc and a weak
molecular gas clump structure at a distance of around 460 pc from the nucleus.
Observations of the first two CO transitions allowed us to compute the line
ratio, and the average I_{21}/I_{10} ratio is 0.68 for the M~81 center. This
low value, atypical both of the galactic nuclei of spiral galaxies and of
interacting systems, is probably associated to diffuse gas with molecular
hydrogen density that is not high enough to excite the CO molecules. After
analyzing the clumping properties of the molecular gas in detail, we identify
very massive giant molecular associations (GMAs) in CO(2-1) emission with
masses of 10 M and diameters of 250 pc. The deduced
N(H_{2})/I_{CO} ratio for the individually resolved GMAs, assumed to be
virialized, is a factor of 15 higher than the \textit{standard} Galactic
value, showing - as suspected - that the X ratio departs significantly from the
mean for galaxies with an unusual physics of the molecular gas.Comment: 12 pages, 7 figures, 6 tables. Accepted for pubblication in A&
Conduct and reporting of formula milk trials: systematic review
Objective To systematically review the conduct and reporting of formula trials. Design Systematic review. Data sources Medline, Embase, and Cochrane Central Register of Controlled Trials (CENTRAL) were searched from 1 January 2006 to 31 December 2020. Review methods Intervention trials comparing at least two formula products in children less than three years of age were included, but not trials of human breast milk or fortifiers of breast milk. Data were extracted in duplicate and primary outcome data were synthesised for meta-analysis with a random effects model weighted by the inverse variance method. Risk of bias was evaluated with Cochrane risk of bias version 2.0, and risk of undermining breastfeeding was evaluated according to published consensus guidance. Primary outcomes of the trials included in the systematic review were identified from clinical trial registries, protocols, or trial publications. Results 22 201 titles were screened and 307 trials were identified that were published between 2006 and 2020, of which 73 (24%) trials in 13 197 children were prospectively registered. Another 111 unpublished but registered trials in 17 411 children were identified. Detailed analysis was undertaken for 125 trials (23 757 children) published since 2015. Seventeen (14%) of these recently published trials were conducted independently of formula companies, 26 (21%) were prospectively registered with a clear aim and primary outcome, and authors or sponsors shared prospective protocols for 11 (9%) trials. Risk of bias was low in five (4%) and high in 100 (80%) recently published trials, mainly because of inappropriate exclusions from analysis and selective reporting. For 68 recently published superiority trials, a pooled standardised mean difference of 0.51 (range −0.43 to 3.29) was calculated with an asymmetrical funnel plot (Egger’s test P<0.001), which reduced to 0.19 after correction for asymmetry. Primary outcomes were reported by authors as favourable in 86 (69%) trials, and 115 (92%) abstract conclusions were favourable. One of 38 (3%) trials in partially breastfed infants reported adequate support for breastfeeding and 14 of 87 (16%) trials in non-breastfed infants confirmed the decision not to breastfeed was firmly established before enrolment in the trial. Conclusions The results show that formula trials lack independence or transparency, and published outcomes are biased by selective reporting. Systematic review registration PROSPERO 2018 CRD42018091928
High-resolution mapping of the physical conditions in two nearby active galaxies based on 12CO(1-0), (2-1) and (3-2) lines
We present a detailed analysis of high resolution observations of the three
lowest CO transitions in two nearby active galaxies, NGC4569 and NGC4826. The
CO(1-0) and (2-1) lines were observed with the Plateau de Bure Interferometer
and the CO(3-2) line with the Submillimeter Array. Combining these data allows
us to compare the emission in the three lines and to map the line ratios,
R21=I_{CO(2-1)}/I_{CO(1-0)} and R32=I_{CO(3-2)}/I_{CO(1-0)} at a resolution of
~2", i.e., a linear resolution of 160 pc for NGC4569 and 40 pc for NGC4826. In
both galaxies the emission in the three lines is similarly distributed
spatially and in velocity, and CO is less excited (R32<0.6) than in the
Galactic Center or the centers of other active galaxies studied so far.
According to a pseudo-LTE model the molecular gas in NGC4569 is cold and mainly
optically thick in the CO(1-0) and (2-1) lines; less than 50% of the gas is
optically thin in the CO(3-2) line. LVG modeling suggests the presence of an
elongated ring of cold and dense gas coinciding with the ILR of the stellar
bar. More excited gas is resolved in the circumnuclear disk of NGC4826.
According to our pseudo-LTE model this corresponds to warmer gas with a ~50% of
the CO(3-2) emission being optically thin. LVG modeling indicates the presence
of a semicircular arc of dense and cold gas centered on the dynamical center
and ~70 pc in radius. The gas temperature increases and its density decreases
toward the center. A near side/far side asymmetry noticeable in the CO, R32 and
Pa-alpha maps suggests that opacity effects play a role. Examining published CO
maps of nearby active galaxies we find similar asymmetries suggesting that this
could be a common phenomenon in active galaxies. These mainly qualitative
results open new perspectives for the study of active galaxies with the future
Atacama Large Millimeter/submillimeter Array.Comment: accepted for publication in A&
The Energy Density in the Casimir Effect
We compute the expectations of the squares of the electric and magnetic
fields in the vacuum region outside a half-space filled with a uniform
dispersive dielectric. We find a positive energy density of the electromagnetic
field which diverges at the interface despite the inclusion of dispersion in
the calculation. We also investigate the mean squared fields and the energy
density in the vacuum region between two parallel half-spaces. Of particular
interest is the sign of the energy density. We find that the energy density is
described by two terms: a negative position independent (Casimir) term, and a
positive position dependent term with a minimum value at the center of the
vacuum region. We argue that in some cases, including physically realizable
ones, the negative term can dominate in a given region between the two
half-spaces, so the overall energy density can be negative in this region.Comment: 16 pages, 4 figures; 3 references and some new material in Sect. 4.4
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