In situ degradability of dry matter and neutral-detergent fibre of thorn scrubland forage consumed by goats in the semi-arid region of north Mexico

Three goats provided with oesophageal and ruminal cannulae were used to determine variations in dry matter (DM) and neutral-detergent fibre (NDF) degradability of the forage consumed when grazing thorn scrubland in the semi-arid region of north Mexico, during two consecutive dry and wet periods. Ingesta samples were incubated intraruminally, the data were fitted to the exponential equation P = a + b (1-e(-ct)) and statistically analysed using a randomized-block design. Organic matter and crude protein (CP) contents were higher (P < 0.05) in the wet seasons. Values of NDF were similar in dry and wet season of both years whereas higher numerical values of acid-detergent fibre (ADF), lignin and cellulose were registered in the dry seasons. DM and NDF degradabilities after 24 and 48 h of ruminal incubation were higher (P < 0.05) in the wet seasons. Higher values (P < 0.05) in DM and NDF bag losses at zero time (A fraction) were registered in the two wet seasons. The insoluble but fermentable DM and NDF (B fractions) were higher (P < 0.05) in the 1999 wet season and variable in the rest of the studied period. Numerically higher values of DM and NDF c fraction were found in wet periods, whereas DM and NDF potential degradabilities were higher (P < 0.05) in the wet season in 1999 and similar across seasons in 2000. Lowest (P < 0.05) contents of CP in grazed forage, DM and NDF degradabilities after 48 h of ruminal incubation, and A, and B, and c fractions were observed in the dry seasons. Thus, these results may be related to both the lower feeding value of forage consumed by the animals and lower performance of livestock during this period. Then, the DM and NDF degradability after 48 h, together with the insoluble but fermentable matter and the c fraction permit the nutritive value of the forage consumed by grazing goats to be accurately described.

Interactions of KLVFF-PEG peptide conjugate with fibrinogen in neutral aqueous solutions

In this work we report on the interaction of KLVFF-PEG with fibrinogen (Fbg) in neutral aqueous solutions at 20 degrees C, for particular ratios of KLVFF-PEG to Fbg concentration, Delta = CKLVFF-PEG/C-Fbg- Our results show the formation of Fbg/KLVFF-PEG complexes for Delta > 0, such that there is not an extended network of complexes throughout the solution. In addition, cleaved protein and Fbg dimers are identified in the solution for Delta >= 0. There is a dramatic change in the tertiary structure of the Fbg upon KLVFF-PEG binding, although the KLVFF-PEG binds to the Fbg without affecting the secondary structure elements of the glycoprotein.

Intermediate ion stability and regio selectivity polymerization using neutral salicyladiminato in propene nickel(II) and palladium(II) complexes as catalysts

The mechanism of the Heck reaction has been studied with regard to transition metal catalysis of the addition of propene and the formation of unsaturated polymers. The reactivity of nickel and palladium complexes with five different bidentate ligands with O,N donor atoms has been investigated by computational methods involving density functional theory. Hence, it is possible to understand the electronic and steric factors affecting the reaction and their relative importance in determining the products formed in regard of their control of the regiochemistry of the products. Our results show that whether the initial addition of propene is trans to O or to N of the bidentate ligand is of crucial importance to the subsequent reactions. Thus when the propene is trans to 0, 1,2-insertion is favoured, but when the propene is trans to N, then 2,1-insertion is favoured. This difference in the preferred insertion pathway can be related to the charge distribution engendered in the propene moiety when the complex is formed. Indeed charge effects are important for catalytic activity but also for regioselectivity. Steric effects are shown to be of lesser importance even when t-butyl is introduced into the bidentate ligand as a substituent. (C) 2007 Elsevier B.V. All rights reserved.

The crucial importance of agostic interactions in intermediates formed in propylene polymerization using neutral salicyladiminato palladium(II) and nickel complexes as catalysts

The structures of intermediates formed in propylene polymerisation using neutral salicyladiminato palladium(II) and nickel(II) complexes as catalysts have been investigated using density functional theory. Calculations show that all low energy intermediates contain agostic interactions either between the metal and a hydrogen from the added propylene forming four- or five-membered chelate rings, or, when a phenyl ring is present, between the metal and an aromatic C-C bond. The agostic interactions with the metal are concomitant with changes in ligand dimensions and electronic properties. In particular when a metal to hydrogen bond is formed, there is a lengthening of the C-H bond. Significant differences are found for the agostic interactions with palladium and nickel in that for Pd there is a clear preference for specific intermediates but for Ni there are several different structures with similar energies which are likely to lead to a greater variety of products on further polymerisation. (c) 2007 Elsevier B.V. All rights reserved.

A DFT study of propylene polymerization using neutral salicyladiminato nickel(II) and palladium(II) as catalysts

Propylene polymerization using salicyladiminato metal catalalysts has been studied using density functional theory at the B3LYP/LANL2DZ level. In particular, the effects on the reaction mechanisms of changing the metal from Pd(II) to Ni(II) have been investigated. While the reaction mechanisms involving the salicyladiminato Ni(II) catalyst have been found to be similar to those established previously for the salicyladiminato Pd(II) catalyst, the nickel catalyst was found to differentiate the trans-O intermediate from the trans-.N intermediate with an energy difference of 46.63 U mol(-1) significantly more than the palladium catalyst for which the energy difference was calculated as 35.82 kJ mol(-1). The energy difference between the trans-O configuration and the trans-N configuration is decreased significantly when combining a molecule of propylene with the catalyst. For the Ni catalyst, the trans-O isomer is more stable than the trans-N isomer to a greater extent than for Pd, so that the insertion of propylene from 20 is relatively less favoured for Ni than for Pd. It is predicted that the mechanism of isomerization from 20 to 2N through a rotational transition state TS2O2N is more appropriate for the Ni catalyst system. The palladium system shows a larger preference for pi-coordination than its nickel counterpart, although the latter possesses a lower reaction barrier. It was found that the occupation of the trans-O position in the asymmetric salicyladiminato catalyst is also more favored by the alkene as it is by the alkyl so that insertion of the alkene may always start from a particular configuration so that specific products are obtained. (c) 2005 Elsevier B.V. All rights reserved.

Coordination-driven self-assembly of a novel carbonato-bridged heteromolecular neutral nickel(II) triangle by atmospheric CO2 fixation

Formation of a quasi-symmetrical mu(3)-carbonato-bridged self-assembled heteromolecular triangle of Ni(II), [(mu(3)-CO3){Ni-2(salmeNH)(2)(NCS)(2)}[Ni(salmeNH(2))(2)]center dot Et2O center dot H2O (HsalmeNH = 2-[(3-methylamino-propylimino)-methyl]-phenol) involves atmospheric CO2 uptake in a neutral medium, by spontaneous self-reorganization of the starting mononuclear Ni(II)-Schiff-base complex, [Ni(salmeNH)(2)]. The environment around Ni(II) in two of the subunits is different from the third one. The starting complex, (Ni(salmeNH)(2)], and one of the possible intermediate species, [Ni(salmeNH(2))(2)(NCS)(2)], which has a very similar coordination environment to that in the third Ni(II) center, have been characterized structurally. A plausible mechanism for the formation of such a triangle has also been proposed. The compound shows a very strong antiferromagnetic coupling. Fit as a regular triangular arrangement gave J = -53.1, g = 2.24, and R = 1.5 x 10(-4).

Effect of mountain breeze in ventilating the city under calm and neutral atmospheric environment: Interaction of airflow structures and ventilation efficiency

Many modern cities locate in the mountainous areas, like Hong Kong, Phoenix City and Los Angles. It is confirmed in the literature that the mountain wind system developed by differential heating or cooling can be very beneficial in ventilating the city nearby and alleviating the UHI effect. However, the direct interaction of mountain wind with the natural-convection circulation due to heated urban surfaces has not been studied, to our best knowledge. This kind of unique interaction of two kinds of airflow structures under calm and neutral atmospheric environment is investigated in this paper by CFD approach. A physical model comprising a simple mountain and three long building blocks (forming two street canyons) is firstly developed. Different airflow structures are identified within the conditions of different mountain-building height ratios (R=Hm/Hb) by varying building height but fixing mountain height. It is found that the higher ventilation rate in the street canyons is expected in the cases of smaller mountain-building ratios, indicating the stronger natural convection due to increasing heated building surfaces. However, there is the highest air change rate (ACH) in the lowest-building-height case and most of the air is advective into the street canyon through the top open area, highlighting the important role played by the mountain wind. In terms of the ventilation efficiency, it is shown that the smallest R case enjoys the best air change efficiency followed by the highest R case, while the worst ventilative street canyons occur at the middle R case. In the end, a gap across the streets is introduced in the modeling. The existence of the gap can greatly channel the mountain wind and distribute the air into streets nearby. Thus the ACH can be doubled and air quality can be significantly improved.

Voltage-gated potassium currents within the dorsal vagal nucleus: inhibition by BDS toxin

Voltage-gated potassium (Kv) channels are essential components of neuronal excitability. The Kv3.4 channel protein is widely distributed throughout the central nervous system (CNS), where it can form heteromeric or homomeric Kv3 channels. Electrophysiological studies reported here highlight a functional role for this channel protein within neurons of the dorsal vagal nucleus (DVN). Current clamp experiments revealed that blood depressing substance (BDS) and intracellular dialysis of an anti-Kv3.4 antibody prolonged the action potential duration. In addition, a BDS sensitive, voltage-dependent, slowly inactivating outward current was observed in voltage clamp recordings from DVN neurons. Electrical stimulation of the solitary tract evoked EPSPs and IPSPs in DVN neurons and BDS increased the average amplitude and decreased the paired pulse ratio, consistent with a presynaptic site of action. This presynaptic modulation was action potential dependent as revealed by ongoing synaptic activity. Given the role of the Kv3 proteins in shaping neuronal excitability, these data highlight a role for homomeric Kv3.4 channels in spike timing and neurotransmitter release in low frequency firing neurons of the DVN.

Revenue-neutral tax policy under price uncertainty

The firm's response to revenue-neutral taxation is investigated under price uncertainty. Revenue-neutral policies adjust simultaneously the marginal tax rate and the level of exemptions while keeping expected tax receipts constant. Nonincreasing absolute risk aversion is sufficient to sign the firm's response: a reduction in the marginal rate causes the firm to contract output. Implications are established for the equilibrium level of treasury receipts.

Revenue-neutral tax policies under price uncertainty: reply

In their comment on my 1990 article, Yeh, Suwanakul, and Mai extend my analysis-which focused attention exclusively on firm output-to allow for simultaneous endogeneity of price, aggregate output, and numbers of firms. They show that, with downward- sloping demand, industry output adjusts positively to revenue-neutral changes in the marginal rate of taxation. This result is significant for two reasons. First, we are more often interested in predictions about aggregate phenomena than we are in predictions about individual firms. Indeed, firm-level predictions are frequently irrefutable since firm data are often unavailable. Second, the authors derive their result under a set of conditions that appear to be more general than those invoked in my 1990 article. In particular, they circumvent the need to invoke specific assumptions about the nature of firms' aversions toward risk. I consider this a useful extension and I appreciate the careful scrutiny of my paper.

Evidence of neutral transcriptome evolution in plants

The transcriptome of an organism is its set of gene transcripts (mRNAs) at a defined spatial and temporal locus. Because gene expression is affected markedly by environmental and developmental perturbations, it is widely assumed that transcriptome divergence among taxa represents adaptive phenotypic selection. This assumption has been challenged by neutral theories which propose that stochastic processes drive transcriptome evolution. To test for evidence of neutral transcriptome evolution in plants, we quantified 18 494 gene transcripts in nonsenescent leaves of 14 taxa of Brassicaceae using robust cross-species transcriptomics which includes a two-step physical and in silico-based normalization procedure based on DNA similarity among taxa. Transcriptome divergence correlates positively with evolutionary distance between taxa and with variation in gene expression among samples. Results are similar for pseudogenes and chloroplast genes evolving at different rates. Remarkably, variation in transcript abundance among root-cell samples correlates positively with transcriptome divergence among root tissues and among taxa. Because neutral processes affect transcriptome evolution in plants, many differences in gene expression among or within taxa may be nonfunctional, reflecting ancestral plasticity and founder effects. Appropriate null models are required when comparing transcriptomes in space and time.

Tracking the momentum flux of a CME and quantifying its influence on geomagnetically induced currents at Earth

We investigate a coronal mass ejection (CME) propagating toward Earth on 29 March 2011. This event is specifically chosen for its predominately northward directed magnetic field, so that the influence from the momentum flux onto Earth can be isolated. We focus our study on understanding how a small Earth-directed segment propagates. Mass images are created from the white-light cameras onboard STEREO which are also converted into mass height-time maps (mass J-maps). The mass tracks on these J-maps correspond to the sheath region between the CME and its associated shock front as detected by in situ measurements at L1. A time series of mass measurements from the STEREO COR-2A instrument is made along the Earth propagation direction. Qualitatively, this mass time series shows a remarkable resemblance to the L1 in situ density series. The in situ measurements are used as inputs into a three-dimensional (3-D) magnetospheric space weather simulation from the Community Coordinated Modeling Center. These simulations display a sudden compression of the magnetosphere from the large momentum flux at the leading edge of the CME, and predictions are made for the time derivative of the magnetic field (dB/dt) on the ground. The predicted dB/dt values were then compared with the observations from specific equatorially located ground stations and showed notable similarity. This study of the momentum of a CME from the Sun down to its influence on magnetic ground stations on Earth is presented as a preliminary proof of concept, such that future attempts may try to use remote sensing to create density and velocity time series as inputs to magnetospheric simulations.

Cusp ion steps, field-aligned currents and poleward moving auroral forms

We predict the field-aligned currents around cusp ion steps produced by pulsed reconnection between the geomagnetic field and an interplanetary magnetic field (IMF) with a B-Y component that is large in magnitude. For B-Y > 0, patches of newly opened flux move westward and eastward in the Northern and Southern Hemispheres, respectively, under the influence of the magnetic curvature force. These flow directions are reversed for B-Y < 0. The speed of this longitudinal motion initially grows with elapsed time since reconnection, but then decays as the newly opened field lines straighten. We predict sheets of field-aligned current on the boundaries between the patches produced by successive reconnection pulses, associated with the difference in the speeds of their longitudinal motion. For low elapsed times since reconnection, near the equatorward edge of the cusp region where the field lines are accelerating, the field-aligned current sheets will be downward or upward in both hemispheres for positive or negative IMF B-Y, respectively. At larger elapsed times since reconnection, as events slow and evolve from the cusp into the mantle region, these field-aligned current directions will be reversed. Observations by the Polar spacecraft on August 26,1998, show the predicted upward current sheets at steps seen in the mantle region for IMF B-Y > 0. Mapped into the ionosphere, the steps coincide with poleward moving events seen by the CUTLASS HF radar. The mapped location of the largest step also coincides with a poleward moving arc seen by the UVI imager on Polar. We show that the arc is consistent with a region of upward field-aligned current that has become unstable, such that a potential drop of about 1 kV formed below the spacecraft. The importance of these observations is that they confirm that the poleward moving events, as seen by the HF radar and the UV imager, are due to pulsed magnetopause reconnection. Milan et al. [2000] noted that the great longitudinal extent of these events means that the required reconnection pulses would have contributed almost all the voltage placed across the magnetosphere at this time. The observations also show that auroral arcs can form on open field lines in response to the pulsed application of voltage at the magnetopause.