315 research outputs found
The heat of atomization of sulfur trioxide, SO - a benchmark for computational thermochemistry
Calibration ab initio (direct coupled cluster) calculations including basis
set extrapolation, relativistic effects, inner-shell correlation, and an
anharmonic zero-point energy, predict the total atomization energy at 0 K of
SO to be 335.96 (observed 335.920.19) kcal/mol. Inner polarization
functions make very large (40 kcal/mol with , 10 kcal/mol with
basis sets) contributions to the SCF part of the binding energy. The molecule
presents an unusual hurdle for less computationally intensive theoretical
thermochemistry methods and is proposed as a benchmark for them. A slight
modification of Weizmann-1 (W1) theory is proposed that appears to
significantly improve performance for second-row compounds.Comment: Chem. Phys. Lett., in pres
The ground-state spectroscopic constants of Be_2 revisited
Extensive ab initio calibration calculations combined with extrapolations
towards the infinite-basis limit lead to a ground-state dissociation energy of
Be_2, D_e=944 \pm 25 1/cm, substantially higher than the accepted experimental
value, and confirming recent theoretical findings. Our best computed
spectroscopic observables (expt. values in parameters) are G(1)-G(0)=223.7
(223.8), G(2)-G(1)=173.8 (169 \pm 3), G(3)-G(2)=125.4 (122 \pm 3), and
B_0=0.6086 (0.609) 1/cm; revised spectroscopic constants are proposed.
Multireference calculations based on a full valence CAS(4/8) reference suffer
from an unbalanced description of angular correlation; for the utmost accuracy,
a CAS(4/16) reference including the orbitals is required, while for
less accurate work a CAS(4/4) reference is recommended. The quality of computed
coupled cluster results depends crucially on the description of connected
triple excitations; the CC5SD(T) method yields unusually good results because
of an error compensation.Comment: Chem. Phys. Lett., in pres
Heats of formation of perchloric acid, HClO, and perchloric anhydride, ClO. Probing the limits of W1 and W2 theory
The heats of formation of HClO and ClO have been determined to
chemical accuracy for the first time by means of W1 and W2 theory. These
molecules exhibit particularly severe degrees of inner polarization, and as
such obtaining a basis-set limit SCF component to the total atomization energy
becomes a challenge. (Adding high-exponent functions to a standard
basis set has an effect on the order of 100 kcal/mol for ClO.) Wilson's
aug-cc-pV(n+d)Z basis sets represent a dramatic improvement over the standard
aug-cc-pVnZ basis sets, while the aug-cc-pVnZ+2d1f sequence converges still
more rapidly. Jensen's polarization consistent basis sets still require
additional high-exponent functions: for smooth convergence we suggest the
\{aug-pc1+3d,aug-pc2+2d,aug-pc3+d,aug-pc4\} sequence. The role of the tight
functions is shown to be an improved description of the Cl (3d) Rydberg
orbital, enhancing its ability to receive back-bonding from the oxygen lone
pairs. In problematic cases like this (or indeed in general), a single
SCF/aug-cc-pV6Z+2d1f calculation may be preferable over empirically motivated
extrapolations. Our best estimate heats of formation are HClO(g)1 kcal/mol and ClO(g)2 kcal/mol, the largest source of
uncertainty being our inability to account for post-CCSD(T) correlation
effects. While G2 and G3 theory have fairly large errors, G3X theory reproduces
both values to within 2 kcal/mol.Comment: J. Mol. Struct. (THEOCHEM), in press (WATOC'05 special issue
Anharmonic force fields of perchloric acid, HClO, and perchloric anhydride, ClO. An extreme case of inner polarization
DFT (density functional theory) anharmonic force fields with basis sets near
the Kohn-Sham limit have been obtained for perchloric acid, HClO, and
perchloric anhydride, ClO. Calculated fundamental frequencies are in
very good agreement with available experimental data. Some reassignments in the
vibrational spectra of ClO are proposed based on our calculations.
HClO and ClO are particularly severe examples of the `inner
polarization' phenomenon. The polarization consistent basis sets pc-1 and pc-2
(as well as their augmented counterparts) should be supplemented with two
(preferably three) and one (preferably two) high-exponent functions,
respectively, on second-row atoms. Complete anharmonic force fields are
available as electronic supporting information.Comment: J. Mol. Struct., in press (special issue); Electronic Supporting
Information at http://theochem.weizmann.ac.il/web/papers/Cl2O7.htm
Non-invasive assessment of the reproductive cycle in free-ranging female African elephants (Loxodonta africana) treated with a gonadotropin-releasing hormone (GnRH) vaccine for inducing anoestrus
BACKGROUND: In southern Africa, various options to manage elephant populations are being considered.
Immunocontraception is considered to be the most ethically acceptable and logistically feasible method for control
of smaller and confined populations. In this regard, the use of gonadotropin-releasing hormone (GnRH) vaccine has
not been investigated in female elephants, although it has been reported to be safe and effective in several
domestic and wildlife species. The aims of this study were to monitor the oestrous cycles of free-ranging African
elephant cows using faecal progestagen metabolites and to evaluate the efficacy of a GnRH vaccine to induce
anoestrus in treated cows.
METHODS: Between May 2009 - June 2010, luteal activity of 12 elephant cows was monitored non-invasively using
an enzyme immunoassay detecting faecal 5alpha-reduced pregnanes (faecal progestagen metabolites, FPM) on a
private game reserve in South Africa. No bulls of breeding age were present on the reserve prior to and for the
duration of the study. After a 3-month control period, 8 randomly-selected females were treated twice with 600
micrograms of GnRH vaccine (ImprovacW, Pfizer Animal Health, Sandton, South Africa) 5-7 weeks apart. Four of
these females had been treated previously with the porcine zona pellucida (pZP) vaccine for four years (2004-2007).
RESULTS: All 12 monitored females (8 treated and 4 controls) showed signs of luteal activity as evidenced by FPM
concentrations exceeding individual baseline values more than once. A total of 16 oestrous cycles could be
identified in 8 cows with four of these within the 13 to 17 weeks range previously reported for captive African
elephants. According to the FPM concentrations the GnRH vaccine was unable to induce anoestrus in the treated
cows. Overall FPM levels in samples collected during the wet season (mean 4.03 micrograms/gram dry faeces) were
significantly higher (P<0.002) than the dry season (mean 2.59 micrograms/gram dry faeces).
CONCLUSIONS: The GnRH vaccination protocol failed to induce anoestrus in the treated female elephants. These
results indicate that irregular oestrous cycles occur amongst free-ranging elephants and are not restricted to
elephants in captivity. The relationship between ecological conditions and endocrine activity were confirmed.
Free-ranging female elephants were observed to not cycle continuously throughout the year in the absence of
adult bulls.http://www.rbej.com/content/10/1/63ab2012ab2013 (Author correction)ab2013 (Author correction
Vaccination against GnRH as a prelude to surgical castration of horses
BACKGROUND : Surgical castration is one of the most frequently performed surgeries in horses and is associated with various post-surgical complications ranging in severity. OBJECTIVES : We investigated the effects of administering an anti-GnRH vaccine to colts for reduction of testis size on the incidence of complications associated with their subsequent surgical castration. STUDY DESIGN : Randomised open controlled trial. METHODS : Nineteen colts were randomly assigned to one of the three groups. Treatment Groups V1-57 and V2-100 received two treatments of Improvac® (Zoetis, South Africa) before their castration in the field on either Day 57 or Day 100 following first treatment, respectively. Controls similarly received placebo treatments followed by castration on Day 57. Serial measurements of testicular dimensions and serum samples for measuring serum testosterone concentrations (STCs) and anti-GnRH antibody titres (ABTs) were obtained pre- and post-vaccination and on the day of castration. Clinical data recorded for 10 days determined post-surgical complications. RESULTS : All vaccinated colts showed a baseline STC concentration at castration with a strong ABT response. Mean testicular volume of Groups V1-57 and V2-100 reduced by 49.7% and 30.8%, respectively, on Day 57 and this further reduced in Group V2-100 by 63.9% at castration on Day 100. Testis size was significantly correlated with post-surgical preputial (P = 0.001) and scrotal (P = 0.025) swelling. MAIN LIMITATIONS : A study population of young light horse breed colts and a relatively small sample size limited this pilot study.http://www.wileyonlinelibrary.com/journal/evj2021-12-22hj2021Mammal Research InstituteProduction Animal StudiesZoology and Entomolog
Reversibility of the effects of GnRH-vaccination used to suppress reproductive function in mares
Reasons for performing study: Active immunisation against gonadotrophin-releasing
hormone (GnRH) provides a reversible method for control of oestrous behaviour and fertility
in mares. Previous reports failed to demonstrate the interval to resumption of cyclic ovarian
activity after GnRH-vaccination.
Hypothesis: Administration of the GnRH-vaccine ImprovacÒ1 in a large group of mares of
various ages will result in effective, reliably reversible suppression of ovarian activity within
a two-year period.
Methods: The mares, subdivided into three age categories were vaccinated twice (with a 35 d
interval) using ImprovacÒ1 and were monitored via blood samples until Day 720 after initial
vaccination for serum progesterone concentration determination by radio-immune assay and
anti-GnRH antibody titre by enzyme immuno-assay. Samples were collected until individuals
resumed cyclic ovarian activity.
Results: All mares showed suppression of cyclic ovarian activity (SPC <1 nmol/l) and 92.2%
resumed cyclic activity at Day 720 with a mean interval = 417.8 d (SD = 23.19) and median =
344 d. A significant age effect (P=0.028) on the interval, but not on GnRH-AB titre response,
was observed between the youngest (11 years) categories. Conclusions: Immunising adult mares of all ages with ImprovacÒ1 resulted in a reversible
suppression of cyclic ovarian activity in most mares. An age effect, with the youngest mares
showing a longer interval to reversibility was observed.The Equine Research Centre of the University of Pretoriahttp://www.evj.co.uk/journals/hb2013ab201
Machine learning algorithms performed no better than regression models for prognostication in traumatic brain injury
Objective: We aimed to explore the added value of common machine learning (ML) algorithms for prediction of outcome for moderate and severe traumatic brain injury. Study Design and Setting: We performed logistic regression (LR), lasso regression, and ridge regression with key baseline predictors in the IMPACT-II database (15 studies, n = 11,022). ML algorithms included support vector machines, random forests, gradient boosting machines, and artificial neural networks and were trained using the same predictors. To assess generalizability of predictions, we performed internal, internal-external, and external validation on the recent CENTER-TBI study (patients with Glasgow Coma Scale <13, n = 1,554). Both calibration (calibration slope/intercept) and discrimination (area under the curve) was quantified. Results: In the IMPACT-II database, 3,332/11,022 (30%) died and 5,233(48%) had unfavorable outcome (Glasgow Outcome Scale less than 4). In the CENTER-TBI study, 348/1,554(29%) died and 651(54%) had unfavorable outcome. Discrimination and calibration varied widely between the studies and less so between the studied algorithms. The mean area under the curve was 0.82 for mortality and 0.77 for unfavorable outcomes in the CENTER-TBI study. Conclusion: ML algorithms may not outperform traditional regression approaches in a low-dimensional setting for outcome prediction after moderate or severe traumatic brain injury. Similar to regression-based prediction models, ML algorithms should be rigorously validated to ensure applicability to new populations
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