High Ka Research Articles

A direct numerical simulation study of flame structure and stabilization of an experimental high Ka CH4/air premixed jet flame

In the present work, a direct numerical simulation (DNS) of an experimental high Karlovitz number (Ka) CH4/air piloted premixed flame was analyzed to study the inner structure and the stabilization mechanism of the turbulent flame. A reduced chemical mechanism for premixed CH4/air combustion with NOx based on GRI-Mech3.0 was used, including 268 elementary reactions and 28 transported species. The evolution of the stretch factor, I0, indicates that the burning rate per unit flame surface area is considerably reduced in the near field and exhibits a minimum at x/D = 8. Downstream, the burning rate gradually increases. The stretch factor is different between different species, suggesting the quenching of some reactions but not others. Comparison between the turbulent flame and strained laminar flames indicates that certain aspects of the mean flame structure can be represented surprisingly well by flamelets if changes in boundary conditions are accounted for and the strain rate of the mean flow is employed; however, the thickening of the flame due to turbulence is not captured. The spatial development of displacement speeds is studied at higher Ka than previous DNS. In contrast to almost all previous studies, the mean displacement speed conditioned on the flame front is negative in the near field, and the dominant contribution to the displacement speed is normal diffusion with the reaction contribution being secondary. Further downstream, reaction overtakes normal diffusion, contributing to a positive displacement speed. The negative displacement speed in the near field implies that the flame front situates itself in the pilot region where the inner structure of the turbulent flame is affected significantly, and the flame stabilizes in balance with the inward flow. Notably, in the upstream region of the turbulent flame, the main reaction contributing to the production of OH, H+O2⇔O+OH (R35), is weak. Moreover, oxidation reactions, H2+OH⇔H+H2O (R79) and CO+OH⇔CO2+H (R94), are influenced by H2O and CO2 from the pilot and are completely quenched. Hence, the entire radical pool of OH, H and O is affected. However, the fuel consumption layer remains comparably active and generates heat, mainly via the reaction CH4+OH⇔CH3+H2O (R93).

The impact of obesity on compensatory mechanisms in response to progressive sagittal malalignment

Background ContextObesity's impact on standing sagittal alignment remains poorly understood, especially with respect to the role of the lower limbs. Given energetic expenditure in standing, a complete understanding of compensation in obese patients with sagittal malalignment remains relevant. PurposeThis study compares obese and non-obese patients with progressive sagittal malalignment for differences in recruitment of pelvic and lower-limb mechanisms. Study Design/SettingSingle-center retrospective review. Patient SampleA total of 554 patients (277 obese, 277 non-obese) were identified for analysis. Outcome MeasuresUpper body alignment parameters: sagittal vertical axis (SVA) and T1 spinopelvic inclination (T1SPi). Compensatory lower-limb mechanisms: pelvic translation (pelvic shift [PS]), knee (KA) and ankle (AA) flexion, hip extension (sacrofemoral angle [SFA]), and global sagittal angle (GSA). MethodsInclusion criteria were patients ≥18 years who underwent full-body stereographic x-rays. Included patients were categorized as non-obese (N-Ob: body mass index [BMI]<30 kg/m2) or obese (Ob: BMI≥30 kg/m2). To control for potential confounders, groups were propensity score matched by age, gender, and baseline pelvic incidence (PI), and subsequently categorized by increasing spinopelvic (pelvic incidence minus lumbar lordosis [PI−LL]) mismatch: <10°, 10°–20°, >20°. Independent t tests and linear regression models compared sagittal (SVA, T1SPi) and lower limb (PS, KA, AA, SFA, GSA) parameters between obesity cohorts. ResultsA total of 554 patients (277 Ob, 277 N-Ob) were included for analysis and were stratified to the following mismatch categories: <10°: n=367; 10°–20°: n=91; >20°: n=96. Obese patients had higher SVA, KA, PS, and GSA than N-Ob patients (p<.001 all). Low PI−LL mismatch Ob patients had greater SVA with lower SFA (142.22° vs. 156.66°, p=.032), higher KA (5.22° vs. 2.93°, p=.004), and higher PS (4.91 vs. −5.20 mm, p<.001) than N-Ob patients. With moderate PI−LL mismatch, Ob patients similarly demonstrated greater SVA, KA, and PS, combined with significantly lower PT (23.69° vs. 27.14°, p=.012). Obese patients of highest (>20°) PI−LL mismatch showed greatest forward malalignment (SVA, T1SPi) with significantly greater PS, and a concomitantly high GSA (12.86° vs. 9.67°, p=.005). Regression analysis for lower-limb compensation revealed that increasing BMI and PI−LL predicted KA (r2=0.234) and GSA (r2=0.563). ConclusionsWith progressive sagittal malalignment, obese patients differentially recruit lower extremity compensatory mechanisms, whereas non-obese patients preferentially recruit pelvic mechanisms. The ability to compensate for progressive sagittal malalignment with the pelvic retroversion is limited by obesity.

Interaction of the HIV NCp7 Protein with Platinum(II) and Gold(III) Complexes Containing Tridentate Ligands.

The human immunodeficiency virus (HIV) nucleocapsid protein (NCp7) plays significant roles in the virus life cycle and has been targeted by compounds that could lead to its denaturation or block its interaction with viral RNA. Herein, we describe the interactions of platinum(II) and gold(III) complexes with NCp7 and how the reactivity/affinity of potential inhibitors can be modulated by judicious choice of ligands. The interactions of [MCl(N3)]n+ (M = Pt2+ (n = 1) and Au3+ (n = 2); N3 = tridentate chelate ligands: bis(2-pyridylmethyl)methylamine (Mebpma, L1) and bis(2-pyridylmethyl)amine (bpma, L2) with the C-terminal zinc finger of NCp7 (ZF2) were investigated by electrospray ionization-mass spectroscopy (ESI-MS). Mass spectra from the incubation of [MCl(Mebpma)]n+ complexes (PtL1 and AuL1) with ZF2 indicated that they were more reactive than the previously studied diethylenetriamine-containing analogues [MCl(dien)]n+. The initial product of reaction of PtL1 with ZF2 results in loss of all ligands and release of zinc to give the platinated apopeptide {PtF} (F = apopeptide). This is in contrast to the incubation with [PtCl(dien)]+, in which {Pt(dien)}-peptide adducts are observed. Incubation of the Au3+ complex AuL1 with ZF2 gave AuxFn+ species (x = 1, 2, 4, F = apopeptide) again with loss of all ligands. Furthermore, the formally substitution-inert analogues [Pt(N3)L]2+ (L = 4-methylpyridine (4-pic), 4-dimethylaminopyridine (dmap), and 9-ethylguanine (9-EtGua)) were prepared to examine stacking interactions with N-acetyltryptophan (N-AcTrp), the Trp-containing ZF2, and the "full" two-finger NCp7 itself using fluorescence quenching titration. Use of bpma and Mebpma gave slightly higher affinity than analogous [Pt(dien)L)]2+ complexes. The dmap-containing complexes (PtL1a and PtL2a) had the greatest association constants (Ka) for N-AcTrp and ZF2 peptide. The complex PtL1a had the highest Ka when compared with other known Pt2+ analogues: [Pt(dien)(9-EtGua)]2+ < [Pt(bpma)(9-EtGua)]2+ < [Pt(dien)(dmap)]2+< PtL2a < PtL1a. A Ka value of ca. 40.6 ± 1.0 × 103 M-1 was obtained for the full NCp7 peptide with PtL1a. In addition, the mass spectrum of the interaction between ZF2 and PtL1a confirms formation of a 1:1 PtL1a/ZF2 adduct. The reactivity of selected complexes with sulfur-containing amino acid N-acetylcysteine (N-AcCys) was also investigated by 195Pt and 1H NMR spectroscopy and ESI-MS. The precursor compounds [PtCl(N3)]+ PtL1 and PtL2 reacted readily, whereas their [Pt(N3)L]2+ analogues PtL1a and PtL2a were inert to substitution.

Synthetic assembly of novel avidin-biotin-GlcNAc (ABG) complex as an attractive bio-probe and its interaction with wheat germ agglutinin (WGA)

A tetravalent GlcNAc pendant glycocluster was constructed with terminal biotin through C6 linker. To acquire the multivalent carbohydrate-protein interactions, we synthesized a glycopolymer of tetrameric structure using N-acetyl-d-glucosamine (GlcNAc) as the target carbohydrate by the use of 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMT-MM) as coupling reagent, followed by biotin-avidin complexation leading to the formation of glycocluster of avidin-biotin-GlcNAc conjugate (ABG complex). The dynamic light scattering (DLS) system was implied for size detection and to check the binding affinity of GlcNAc conjugate with a WGA lectin we use fluorometric assay by means of specific excitation of tryptophan at λex 295nm and it was found to be very high Ka∼1.39×107 M−1 in case of ABG complex as compared to GlcNAc only Ka∼1.01×104 M−1 with the phenomenon proven to be due to glycocluster effect.

Using Computational Modeling To Optimize the Design of Antibodies That Trap Viruses in Mucus.

Immunoglobulin G (IgG) antibodies that trap viruses in cervicovaginal mucus (CVM) via adhesive interactions between IgG-Fc and mucins have recently emerged as a promising strategy to block vaginally transmitted infections. The array of IgG bound to a virus particle appears to trap the virus by making multiple weak affinity bonds to the fibrous mucins that form the mucus gel. However, the antibody characteristics that maximize virus trapping and minimize viral infectivity remain poorly understood. Toward this goal, we developed a mathematical model that takes into account physiologically relevant spatial dimensions and time scales, binding, and unbinding rates between IgG and virions and between IgG and mucins, as well as the respective diffusivities of virions and IgG in semen and CVM. We then systematically explored the IgG-antigen and IgG-mucin binding and unbinding rates that minimize the flux of infectious HIV arriving at the vaginal epithelium. Surprisingly, contrary to common intuition that infectivity would drop monotonically with increasing affinities between IgG and HIV, and between IgG and mucins, our model suggests maximal trapping of HIV and minimal flux of HIV to the epithelium are achieved with IgG molecules that exhibit (i) rapid antigen binding (high kon) rather than very slow unbinding (low koff), that is, high-affinity binding to the virion, and (ii) relatively weak affinity with mucins. These results provide important insights into the design of more potent "mucotrapping" IgG for enhanced protection against vaginally transmitted infections. The model is adaptable to other pathogens, mucosal barriers, geometries, and kinetic and diffusional effects, providing a tool for hypothesis testing and producing quantitative insights into the dynamics of immune-mediated protection.

Kinetic characterization of small DNA-binding molecules interacting with a DNA strand on a quartz crystal microbalance

Quantitative studies of the binding of various DNA-binding antibiotics with dsDNA are useful for drug design, not only for effective antibiotics, but also for antitumor drugs. We studied the binding kinetics, association and dissociation rate constants, and association constants (kon, koff, and Ka, respectively) of intercalators and groove binders, including various antibiotics, to double-stranded DNA (dA30·dT30 and dG30·dC30) immobilized on a highly sensitive 27 MHz quartz-crystal microbalance (QCM) in aqueous solution. Although a simple ethidium bromide intercalator bound to both dA30·dT30 and dG30·dC30, antibiotics that are side-binding intercalators, such as daunomycin, aclacinomycin A, and actinomycin D, with sugar or peptide moieties on the intercalator parts selectively bound to dG30·dC30 with high Ka and small koff values. Nogalamycin, a dumbbell-shaped penetrating intercalator, showed low kon and koff values owing to slow duplex unwinding during the penetration process. Groove binders (Hoechst 33258, distamycin A, and mithramycin) had high Ka values owing to the high kon values. Kinetic parameters depended largely on molecular shapes and DNA-binding molecule binding modes.

Measuring the Kinetics of the Binding of Xenoestrogens and Estrogen Receptor Alpha by Fluorescence Polarization

The mechanism of endocrine disruption by environmental xenoestrogens is unclear. Bisphenol-A (BPA) is an example. Its concentration in human serum is low, and its binding with estrogen receptor (ER) is weak. Yet its effect on prostate and mammary gland development was observed. We investigated whether this effect could be explained in terms of binding kinetics. We used the method of fluorescence polarization anisotropy to measure the kinetic rate constants of the binding of ERα with 19 xenoestrogens. Relative binding affinities (RBA) were also deduced from the kinetics. We drew three observations. First, our RBAs were consistent with published values, thus establishing the validity of our results. Second, our method allowed the determination of low RBAs (∼ 10(-4)) of lipophilic ligands, such as dibutyl phthalate. They could not be measured by steady-state IC50 assays because of their low solubility. Third, we found that BPA had a surprisingly high kon > 10(4) M(-1) s(-1). While its RBA was 1500 times lower than that of 17β estradiol (E2), its kon was >1/90 that of E2. As a result, a 10 min surge of BPA from pM to nM could drive the fraction of BPA-activated ERα to a potent 0.1%. This might help to explain the observable estrogenic impacts of BPA.

Austrian satellite ground station for the Alphasat Q/V band experiments

The bandwidth demand in radio communications is increasing every year, not only in the terrestrial domain, but also in the satellite domain. The Ku Band is already at its capacity limit and the higher Ka Band is filling rapidly and will reach its capacity limit in the years to come. From both the research and commercial point of view it is important to explore the next frontier for satellite communication, which is the Q/V band. In radio communication it is not only a simple up-scaling of the frequency to achieve the same gain with smaller antennas as with bigger antennas in lower bands, but it is the challenge to handle the different wave propagation properties of these higher bands. In Q/V band the atmospheric attenuations are changing quicker than in lower bands (up to 3 dB/s) and the scintillation caused by gas density changes are in the region of 1 Hz with amplitudes of up to 2 dB.

PFC Formation in Aluminium Producing Cells during Normal Electrolysis Potentials

Perfluorocarbons (PFCs) are potent greenhouse gases (GHG) with long lifetimes and high global warming potentials, giving them a high capacity to inflict harm on the environment. The aluminium industry is one of the bigger emitters of these gases and consequently a lot of effort has been put into understanding the mechanism behind the emissions. Aluminium is produced electrochemically by consuming alumina (dissolved in molten cryolite) and carbon. In addition to aluminium this also produces CO2 with a fraction of CO. The reversible potential for the reaction is about 1.2 V, but due to overpotentials related to the electrodes and IR drops in different parts of the cell, especially from the electrolyte, a regular industrial cell needs to operate at a much higher voltage (3.8 – 4.5 V). If the alumina concentration in the electrolyte gets too low the polarisation increases which opens the possibility for other anode reactions, like the production of the PFC gases CF4 and C2F6. The phenomenon is termed anode effect (AE) and traditionally when this occurred the voltage could raise to levels of 20 V or higher, and the current distribution over the anodes would become erratic.In recent years, however, these PFC gases have been discovered at several large, high kA, smelters in China [1-3]. It has been proposed that less uniformity in dissolved alumina for larger cells may elevate individual anode overvoltage sufficiently to produce PFC. The large size gives the cell the ability to distribute the current of the PFC producing anode to the remaining anodes without passing the critical current density.Low cell voltage (LCV) PFC formation was monitored after the dry scrubber on a train of 28 cells at a relatively small Norwegian smelter running at approximately 215 kA. For this work a fourier-transform infrared spectrometer was used. Equipped with a mercury cadmium telluride (MCT) detector and retrofitted with a 35 m / 11 l measurement cell it was possible to get the detection limit down in the low ppb range needed for this study.It was discovered that also small cells could emit PFC that was not directly related to the conventional anode effect. Low cell voltage PFC was found to be discrete emissions mostly in the form of CF4; however, the results indicate that C2F6may also form outside the main anode effect. The emissions can be short lived and self-terminate, but they can also endure for a substantial amount of time and end up in a conventional anode effect, as can be seen from Figure 1.

Activities of Vernonia amygdalina on the fate of metformin in rabbits

The use of herbal preparations in parallel with conventional drugs is on the increase, thus a great concern has arisen. From the leaf of Vernonia amygdalina (VA), several flavones have been isolated:- luteolin, luteolin 7-O-β-glucoside and luteolin 7-O-β-glucuronoside. It is one of the most widely used herbal remedies by diabetic patient with an encouraging safety profile and has been claimed by herbal practitioners to increase the efficacy of an anti-diabetic drug, metformin (MET). Thus we investigated the effect of the aqueous extract of VA on the fate of MET in rabbits. The Pharmacokinetics of MET (100 mg/kg b.wt., o.r.) was studied in rabbits with or without co-administration of the extract of VA (500 mg/kg b.wt., o.r.). Blood samples were drawn at 0h and at 0.5 to 24h post dosing from the retro orbital plexus into sodium heparin bottles and centrifuged to separate plasma. The animals were allowed food after 4h post dose. The plasma samples were assayed for MET levels using validated HPLC method. SPSS 15 statistical package with P set at 0.05 was used to analyzed data. Following VA co-administration, MET showed significantly higher Ka, F, Cmax, AUC0-∞ and Tmax than the control group. No significant difference was seen in t1/2el between the groups. These results indicated that VA enhanced absorption constant Ka thus increasing Cmax. Therefore patients on MET therapy should consume VA with caution as life threatening interaction may occur.

A magic bullet to specifically eliminate mutated mitochondrial genomes from patients' cells

When mitochondrial diseases result from mutations found in the mitochondrial DNA, engineered mitochondrial-targeted nucleases such as mitochondrial-targeted zinc finger nucleases are shown to specifically eliminate the mutated molecules, leaving the wild-type mitochondrial DNA intact to replicate and restore normal copy number. In this issue, Gammage and colleagues successfully apply this improved technology on patients' cells with two types of genetic alterations responsible for neuropathy ataxia and retinitis pigmentosa (NARP) syndrome and Kearns Sayre syndrome and progressive external ophthalmoplegia (PEO).

CW-Cavity Ring Down Spectroscopy of deuterated water in the 1.58 μm atmospheric transparency window

The spectrum of water vapour enriched in deuterium has been recorded by highly sensitive CW-Cavity Ring Down Spectroscopy in the 5855–6802cm−1 spectral region. The studied region includes the 1.58µm atmospheric transparency window of particular interest for remote sensing. More than 8000 absorption lines belonging to eight water isotopologues – H216O, H218O HD16O, D216O, HD18O, D218O, HD17O and D217O – were identified.The spectrum was assigned using both the IUPAC database of experimental transitions and energy levels, and accurate variational calculations. Overall, 1396 and 1277 experimental energy levels belonging to 18 and 16 upper vibrational states were retrieved for the HD16O and D216O species, respectively. 773 energy levels are newly derived. New experimental information concerns the high J (up to 20) and high Ka (up to 12) energy levels of the (101), (021), (040), (210), (120) states of HD16O and of the (111), (031), (210), (012), (130) states of D216O. While only a few energy levels were available, the rotational structure of the (130) and (220) states of HD16O could be analysed in detail. Rotational sublevels of the (140) state of D216O are reported for the first time. A detailed comparison of the derived energy levels with the values recommended by an IUPAC task group is presented. In particular, a significant improvement is evidenced for a number of quasi degenerate energy levels of HD16O. The obtained results are also discussed in relation with several recent studies.

Immobilized glycosylated Fmoc-amino acid for SPR: comparative studies of lectin-binding to linear or biantennary diLacNAc structures

A method to immobilize glycan-linked amino acids with protected α-amino groups, which are key intermediates to produce the desired neoglycoprotein, to a Biacore sensor chip was developed and its utility for interaction analyses was demonstrated. Two types of diN-acetyllactosamine (diLacNAc)-containing glycans, a core 2 hexasaccharide involving linear diLacNAc that is O-linked to N-(9-fluorenyl)methoxycarbonyl (Fmoc)-Thr and a biantennary diLacNAc that is N-linked to Fmoc-Asn, were used as ligands. For immobilization, the free carboxyl groups of the amino acid residues were activated with EDC/NHS, then reacted with the ethylenediamine-derivatized carboxymethyldextran sensor chip to obtain the desired ligand concentrations. Interactions of the ligands with five plant lectins were analyzed by surface plasmon resonance, and the bindings were compared. The resonance unit of each lectin was corrected by subtracting that of the reference cell on which the Fmoc-Thr-core 1 or Fmoc-Asn was immobilized as a ligand. The carbohydrate specificities of interactions were verified by preincubating lectins with their respective inhibitory sugar before injection. By steady state analysis, the Lycopersicon esculentum lectin showed a 27-fold higher affinity to linear diLacNAc than to biantennary diLacNAc, while Datura stramonium and Solanum tuberosum lectins both showed low Ka,apps of 106M−1 for these two ligands. In contrast, Ricinus communis agglutinin-120 showed a 3.2-fold higher Ka,app to biantennary LacNAc than to linear diLacNAc. A lectin purified from Pleurocybella porrigens mushroom interacted at the high affinity of 108M−1 with both linear and biantennary diLacNAcs, which identified it as a unique probe. This method provides a useful and sensitive system to analyze interactions by simulating the glycans on the cell surface.

Kinetic features of the adsorption of sodium oleate on talc

Kinetic features of the adsorption of sodium oleate on dispersed talc samples of Onotskoe deposit are studied. It is shown that adsorption proceeds in two steps with different rate constants of adsorption ka and desorption kd. It is found that at the first step, lasting for nearly one hour under experimental conditions, the process is characterized by high ka and kd values (1.23 × 10−2 m2/(mol min) and 1.06 × 10−5 m2/(L min), respectively). It is concluded that the final stage associated with the rearrangement of molecules on a talc surface lasts for a long time with ka = 2.12 × 10−3 m2/(mol min) and kd = 1.82 × 10−6 m2/(L min).

Locally Duplicated Ohnologs Evolve Faster Than Nonlocally Duplicated Ohnologs in Arabidopsis and Rice

Whole-genome duplications (WGDs) have recurred in the evolution of angiosperms, resulting in many duplicated chromosomal segments. Local gene duplications are also widespread in angiosperms. WGD-derived duplicates, that is, ohnologs, and local duplicates often show contrasting patterns of gene retention and evolution. However, many genes in angiosperms underwent multiple gene duplication events, possibly by different modes, indicating that different modes of gene duplication are not mutually exclusive. In two representative angiosperm genomes, Arabidopsis (Arabidopsis thaliana) and rice (Oryza sativa), we found that 9.6% and 11.3% of unique ohnologs, corresponding to 15.5% and 17.1% of ohnolog pairs, were also involved in local duplications, respectively. Locally duplicated ohnologs are widely distributed in different duplicated chromosomal segments and functionally biased. Coding sequence divergence between duplicated genes is denoted by nonsynonymous (Ka) and synonymous (Ks) substitution rates. Locally duplicated ohnolog pairs tend to have higher Ka, Ka/Ks, and gene expression divergence than nonlocally duplicated ohnolog pairs. Locally duplicated ohnologs also tend to have higher interspecies sequence divergence. These observations indicate that locally duplicated ohnologs evolve faster than nonlocally duplicated ohnologs. This study highlights the necessity to take local duplications into account when analyzing the evolutionary dynamics of ohnologs.

More on Global Quenching of Premixed CH4/Diluent/Air Flames by Intense Near-Isotropic Turbulence

In 2002, Yang and Shy reported a global quenching (GQ) criterion of premixed CH4 flames by turbulence characterized by a Karlovitz number (Ka) estimated at reactant temperature and an equivalence ratio (φ).This article re-analyzes such criteria based on a modified Ka estimated at mean temperature of reactants and products together with newly obtained GQ data at even higher Ka. This modified criterion is compared with a recently found ignition transition, which are then used to evaluate the boundary of thin and broken RZ regimes (Ka = 100) proposed by Peters (2000). It is found that flame GQ occurs beyond the broken RZ regime, where critical Ka ≥ 100 at 0.6 ≤φ < 1.3 forms a parabolic curve with the maximum Ka c ≈ 365 occurring possibly near φ = 1, except for very rich flames where Ka c = 28 at φ = 1.45. A simple model is proposed to explain these results.

A computational study of the influence of synaptic cooperativity on synaptic plasticity in a hippocampal CA1 pyramidal cell

We use a computational model to investigate the possible cooperativity between coactive synapses, both within and between input pathways, in determining plasticity outcomes at individual synapses on a hippocampal CA1 pyramidal cell (PC). The detailed compartmental model of the PC, based on a reconstructed morphology, contains distributions of core ion channels that control voltage transients and calcium entry in the soma and dendrites. Of particular note are the increasing density of A-type potassium channels (KA) with distance in the apical dendrites that provide strong filtering of voltage transients, and high-voltage-gated calcium channels (VGCC) in the dendrites and spines that may contribute to calcium entry in spine heads. Groups of spatially diffuse or clustered excitatory synapses on spines in dendritic layers stratum lacunosum-moleculare (SLM), stratum radiatum (SR) and stratum oriens (SO) are stimulated with single spikes or high frequency bursts. Synaptic currents are mediated by AMPA and NMDA receptors. A proportion of the NMDAR-mediated current is carried by calcium ions. As an indicator of likely synaptic plasticity, the peak calcium level (pCa) obtained in each spine head is measured. Figure ​Figure11 shows results from typical simulations. Peak calcium initially is a somewhat linear function of the number of synchronously active synapses, until saturation. The gain is higher if the density of KA is reduced. With VGCCs, pCa becomes a nonlinear, sigmoidal function. Figure 1 Average spine head peak calcium due to single synchronous stimulation of different numbers of synapses in SLM, in four cell configurations (1) high (standard) KA, (2) high KA with VGCC, (3) low (one third) KA, (4) with VGCC. Error bars show standard deviation. ... Other results show that presynaptic burst stimulation is much more effective at raising spine head calcium levels than single stimuli. Similarly, small numbers of coactive synapses on a single oblique dendrite can achieve high pCa. Activity in one layer, such as SLM can affect pCa in another layer (SR) but only if KA is reduced. In summary, burst stimulation and colocalised activity are most likely to lead to high pCa and hence LTP. Cooperativity across dendritic pathways is possible, but needs specific cellular and stimulation conditions.

Abiotic association of phthalic acid esters with humic acid of a sludge landfill

The abiotic association between phthalic acid esters (PAEs) and humic substances (HS) in sludge landfill plays an important role in the fate and stability of PAEs. An equilibrium dialysis combined with 14C-labeling was used to study the abiotic association of two abundant PAEs (diethyl phthalate and di-n-butyl phthalate) with humic acid (HA) isolated from a sludge landfill with different stabilization times and different molecular weights. Elemental analysis and Fourier Transform Infrared Spectrophotometer (FTIR) suggested that high KA value of HA was related to the high aromatic content and large molecular weight of HA. The results indicated that the association strength of PAEs with HA depended on both the properties of the PAEs and the characteristics of HA. The KA values of the association were strongly dependent on solution pH, and decreased dramatically as the pH was increased from 3.0 to 9.0. The results suggested that nonspecific hydrophobic interaction between PAEs and HA was the main contributor to the association of the PAEs with HA. The interactive hydrogen-bonds between the HA and the PAEs molecules may also be involved in the association.

ChemInform Abstract: Rigidified Macrocyclic Phosphoramides - A New Family of Preorganized Ligands.

Abstract Macrocyclic molecules capable of selective recognition of ionic or neutral guests are of considerable current interest. The design and synthesis of host molecules that contain phosphorus have been developed recently. Typically, the model compound A is modified to the more rigid molecule B which can exist as two exo/endo isomers. B represents a new family of preorganized ligands that can involve the phosphorus group during complexation of various guests. The exo/endo isomerisni was investigated by NMR studies. The complexing properties of B were studied by NMR and extraction method with alkaline and ammonium cations. The complexation constants mainly depend on the molecular geometry and the size of the cavity. The highest Ka constants are obtained with the endo isomer where the P=O bond is directed toward the center of the macrocycle. Complex formation and detailed stereochemical data for A and B will be presented.

Changes in abiotic and biotic phosphorus uptake across a gradient of stream condition

AbstractDegraded streams have been shown to retain fewer nutrients than un‐modified streams. The aim of this project was to investigate the relative importance of abiotic and biotic pathways of phosphorus uptake by epilithic communities in un‐modified and modified streams. This was investigated through a series of filterable reactive phosphorus (FRP)‐uptake experiments in two streams of the Torrens River Catchment, South Australia. Total benthic FRP uptake was assessed as the loss of FRP to un‐sterilized epilithic communities (kT), abiotic uptake was the loss to sterilized epilithic communities (kA) and biotic uptake (kB) was the difference between total and abiotic uptake. It was hypothesized that un‐modified reaches would have higher kA and kB than degraded and engineered reaches. Overall, kT, kA and kB were greatest in un‐modified reaches, but this pattern was not consistent across seasons. kT and kB were greatest in the un‐modified reaches in autumn–winter and late spring, but not in winter–spring. Differences in kB were best explained by phosphorus availability in the water column and the period of continuous flow. kA was greatest in the un‐modified reaches in autumn–winter, greatest in the degraded reaches in winter–spring, but similar in the un‐modified reaches and degraded reaches in late spring. kA was most dependent upon the background FRP concentration, but also the attached organic matter in the un‐modified reaches. The project demonstrated that several impacts of changes in land‐use can alter the affinity of biotic and abiotic processes for phosphorus, which will have implications for in‐stream nutrient availability and downstream ecosystems. Copyright © 2009 John Wiley &amp; Sons, Ltd.