Structure determination of PF3 adsorption on Cu(100) using X-ray standing waves

The local structure of the Cu(100)c(4x2)-PF3 adsorption phase has been investigated through the use of normal-incidence X-ray standing waves (NIXSW), monitored by P 1s and F 1s photoemission, together with P K-edge near-edge X-ray absorption fine structure (NEXAFS). NEXAFS shows the molecule to be oriented with its C3v symmetry axis essentially perpendicular to the surface, while the P NIXSW data show the molecule to be adsorbed in atop sites 2.37±0.04 Å above the surface, this distance corresponding to the Cu-P nearest-neighbour distance in the absence of any surface relaxation. F NIXSW indicates a surprisingly small height difference of the P and F atoms above the surface 0.44±0.06 Å, compared with the value expected for an undistorted gas-phase geometry of 0.77 Å, implying significant increases in the F-P-F bond angles. In addition, however, the F NIXSW data indicate that the molecules have a well-defined azimuthal orientation with a molecular mirror plane aligned in a substrate mirror plane, and with a small (5-10°) tilt of the molecule in this plane such that the two symmetrically-equivalent F atoms in each molecule are tilted down towards the surface

Glutamate 270 plays an essential role in K activation and domain closure of Thermus thermophilus isopropylmalate dehydrogenase

The mutant E270A of Thermus thermophilus 3-isopropylmalate dehydrogenase exhibits largely reduced (∼1%) catalytic activity and negligible activation by K+ compared to the wild-type enzyme. A 3–4 kcal/mol increase in the activation energy of the catalysed reaction upon this mutation could also be predicted by QM/MM calculations. In the X-ray structure of the E270A mutant a water molecule was observed to take the place of K+. SAXS and FRET experiments revealed the essential role of E270 in stabilisation of the active domain-closed conformation of the enzyme. In addition, E270 seems to position K+ into close proximity of the nicotinamide ring of NAD+ and the electron-withdrawing effect of K+ may help to polarise the aromatic ring in order to aid the hydride-transfer

RELAÇÃO ENTRE A DURAÇÃO DO ATO DA INSEMINAÇÃO ARTIFICIAL EM BOVINOS E A FERTILIDADE

The aim of the present experiment was to establish a relationship between the time consumed to perform artificial insemination (AI) and fertility in beef cows. Furthermore, an analysis has been carried out in regard to the inseminators dexterity and the interference of different variables on the number of pregnancies: month, period, time, number of parturitions, body condition, bull, race, temperature. Two groups of Nelore cows from Navirai farms (MS) were used in this experiment. Cows from group I were inseminated during a time no longer than two minutes and cows from group II above two minutes. All cows were healthy and were artificially inseminated only once, the semen being fertile. The detection of the oestrus was performed twice a day, in the morning and the afternoon, with ruffians and in the presence of the inseminators. The length of the insemination has been considered as the time between the drying of the semen pellet, immediately after being melted and its deposition in the uterine body followed by the withdrawal of the universal semen applicator with the sheath from the female genital tract. The diagnosis of gestation has been carried out 60 days after the AI. It has been concluded that the dexterity of the inseminator in carrying on the process itself of AI significantly affects the rate of conception. In regard to the length of time taken to perform AI in bovines it has been found that it interferes in the rate of conception when considered alone (pO presente experimento objetivou estudar a velocidade, em termos de tempo dispendido, à execução da inseminação artificial (IA) propriamente dita, em bovinos de corte, correlacionandose com a fertilidade obtida nos animais pesquisados, bem como verificar a interferência da perícia dos inseminadores quando do ato da IA, além da interferência do conjunto de múltiplas variáveis (mês, período, tempo, número de partos, escore da condição corporal, touro,raça, temperatura) sobre a taxa de prenhez. Utilizou-se dois grupos de vacas da raça Nelore de Fazendas de Naviraí (MS), sendo o grupo I (=animais inseminados em período de tempo de até dois minutos) e o grupo II (= animais inseminados em período de tempo acima de dois minutos). As vacas foram inseminadas artificialmente uma única vez, com sêmen fértil e estavam clinicamente sadias. A detecção do estro era feita duas vezes /dia (manhã e tarde) mediante rufiões e acompanhada pelos inseminadores. A duração do ato inseminatório considerado foi o decorrido entre a secagem da palheta de sêmen, imediatamente após a descongelação, até a retirada do aplicador universal de sêmen com a bainha do trato genital da fêmea, após a deposição do sêmen no corpo uterino. O diagnostico de gestação foi executado 60 dias após a IA. Ao final concluiu-se que a perícia do inseminador ao executar o ato da IA propriamente dito, afeta significativamente a taxa de concepção e que o tempo dispendido à execução do ato da IA nos bovinos, interfere na taxa de concepção, ao ser analisado isoladamente (

A SOMATOTROPINA RECOMBINANTE BOVINA (bST) E A DINÂMICA FOLICULAR EM BOVINOS LEITEIROS

The aim of the present research was to determine the influence of the recombinant bovine somatotropin (bST) on the reproduction of Black and White Holstein bovine females being evaluated along a complete estrous cycle. The follicular dynamics has been observed in regard to the diameter of the ovaries, number of follicular waves during the estrous cycle, duration of each follicular wave, number and diameter of the recruited follicles. Twelve females were used for the experiment, being six of the control group and six of the treated group, chosen at random. The treatment was carried out by administration of a dose of bovine recombinant somatotropin in the sixtieth day post partum (pp). The ovaries follicular dynamics was followed by daily ultrasound exams starting from the day of the first estrus base (visible estrus, considered the 0 day) post partum, until the animals manifested new estrous. In the 60th day the animals of the treated group received an injection of bST (500 mg, SC) and the animals of the group control, 1,4 ml of physiologic solution (SC), as placebo. For the ovarian monitoring of the animals, ultrasound apparel was used with transducer of 5 MHz. It has been observed that the bovine recombinant somatotropin administered in the 2nd month pp, did not display significant influence on the ovarian activity of the animals, the rate of daily milk production being increased only in 3,5%. The studies on the follicular dynamics and the bovine recombinant somatotropin didnt alter the length of the estrous cycle, the diameter of the ovaries, the number of waves follicular, the length of each wave, the number and the diameter of the recruited follicles.O trabalho objetivou determinar a influência da somatotropina recombinante bovina (bST) sobre a reprodução de vacas da raça Holandesa Preta e Branca. Durante um ciclo estral, verificou-se via ultrassonografia, a dinâmica folicular acompanhando-se particularmente o diâmetro dos ovários, o número de ondas foliculares durante o ciclo estral, a duração de cada onda folicular, o número e diâmetro dos folículos recrutados. Foram utilizadas doze fêmeas, sendo seis do grupo controle e seis do grupo tratado, escolhidas ao acaso. O tratamento foi executado mediante administração de uma dose de somatotropina recombinante bovina no sexagésimo dia post partum (pp). A dinâmica folicular dos ovários foi acompanhada por exames ultrassonográficos diários a partir do dia o (estro base e visível) após o parto, até que os animais manifestassem novo cio. No 60º dia os animais do grupo tratado receberam uma injeção de bST (500 mg, SC) e os animais do grupo controle, 1,4 ml de solução fisiológica estéril (SC), como placebo. Para o monitoramento ovariano dos animais, foi utilizado aparelho de ultrassonografia com transdutor de 5 MHz. Concluiu-se que a somatotropina recombinante bovina administrada no 2º mês pp, não exerceu significativa influência sobre a atividade ovariana dos animais, muito embora tenha havido aumento da produção leiteira diária em 3,5% durante o período pesquisado. Os estudos da dinâmica folicular e a somatotropina recombinante bovina não alteraram, o comprimento do ciclo estral, o diâmetro dos ovários, o número de ondas foliculares, o comprimento de cada onda, o número e o diâmetro dos folículos recrutados

Non-Markovian diffusion equations and processes: analysis and simulations

In this paper we introduce and analyze a class of diffusion type equations related to certain non-Markovian stochastic processes. We start from the forward drift equation which is made non-local in time by the introduction of a suitable chosen memory kernel K(t). The resulting non-Markovian equation can be interpreted in a natural way as the evolution equation of the marginal density function of a random time process l(t). We then consider the subordinated process Y(t)=X(l(t)) where X(t) is a Markovian diffusion. The corresponding time evolution of the marginal density function of Y(t) is governed by a non-Markovian Fokker-Planck equation which involves the memory kernel K(t). We develop several applications and derive the exact solutions. We consider different stochastic models for the given equations providing path simulations.Comment: 43 pages, 19 figures, in press on Physica A (2008

Sliding blocks with random friction and absorbing random walks

With the purpose of explaining recent experimental findings, we study the distribution $A(\lambda)$ of distances $\lambda$ traversed by a block that slides on an inclined plane and stops due to friction. A simple model in which the friction coefficient $\mu$ is a random function of position is considered. The problem of finding $A(\lambda)$ is equivalent to a First-Passage-Time problem for a one-dimensional random walk with nonzero drift, whose exact solution is well-known. From the exact solution of this problem we conclude that: a) for inclination angles $\theta$ less than \theta_c=\tan(\av{\mu}) the average traversed distance \av{\lambda} is finite, and diverges when $\theta \to \theta_c^{-}$ as \av{\lambda} \sim (\theta_c-\theta)^{-1}; b) at the critical angle a power-law distribution of slidings is obtained: $A(\lambda) \sim \lambda^{-3/2}$. Our analytical results are confirmed by numerical simulation, and are in partial agreement with the reported experimental results. We discuss the possible reasons for the remaining discrepancies.Comment: 8 pages, 8 figures, submitted to Phys. Rev.