Search

We report high-precision measurements of the deeply virtual Compton scattering (DVCS) cross section at high values of the Bjorken variable x_{B}. DVCS is sensitive to the generalized parton distributions of the nucleon, which provide a three-dimensional description of its internal constituents. Using the exact analytic expression of the DVCS cross section for all possible polarization states of the initial and final electron and nucleon, and final state photon, we present the first experimental extraction of all four helicity-conserving Compton form factors (CFFs) of the nucleon as a function of x_{B}, while systematically including helicity flip amplitudes. In particular, the high accuracy of the present data demonstrates sensitivity to some very poorly known CFFs.

We present new precision measurements of the elastic electron-proton scattering cross section for momentum transfer (Q^{2}) up to 15.75  (GeV/c)^{2}. Combined with existing data, these provide an improved extraction of the proton magnetic form factor at high Q^{2} and double the range over which a longitudinal or transverse separation of the cross section can be performed. The difference between our results and polarization data agrees with that observed at lower Q^{2} and attributed to hard two-photon exchange (TPE) effects, extending to 8  (GeV/c)^{2} the range of Q^{2} for which a discrepancy is established at >95% confidence. We use the discrepancy to quantify the size of TPE contributions needed to explain the cross section at high Q^{2}.

We report measurements of the exclusive neutral pion electroproduction cross section off protons at large values of x_{B} (0.36, 0.48, and 0.60) and Q^{2} (3.1 to 8.4  GeV^{2}) obtained from Jefferson Lab Hall A experiment E12-06-014. The corresponding structure functions dσ_{T}/dt+εdσ_{L}/dt, dσ_{TT}/dt, dσ_{LT}/dt, and dσ_{LT^{'}}/dt are extracted as a function of the proton momentum transfer t-t_{min}. The results suggest the amplitude for transversely polarized virtual photons continues to dominate the cross section throughout this kinematic range. The data are well described by calculations based on transversity generalized parton distributions coupled to a helicity flip distribution amplitude of the pion, thus providing a unique way to probe the structure of the nucleon.

We report measurements of the parity-conserving beam-normal single-spinelastic scattering asymmetries $B_n$ on $^{12}$C and $^{27}$Al, obtained withan electron beam polarized transverse to its momentum direction. Thesemeasurements add an additional kinematic point to a series of previousmeasurements of $B_n$ on $^{12}$C and provide a first measurement on $^{27}$Al.The experiment utilized the Qweak apparatus at Jefferson Lab with a beam energyof 1.158 GeV. The average lab scattering angle for both targets was 7.7degrees, and the average $Q^2$ for both targets was 0.02437 GeV$^2$ (Q=0.1561GeV). The asymmetries are $B_n$ = -10.68 $\pm$ 0.90 stat) $\pm$ 0.57 (syst) ppmfor $^{12}$C and $B_n$ = -12.16 $\pm$ 0.58 (stat) $\pm$ 0.62 (syst) ppm for$^{27}$Al. The results are consistent with theoretical predictions, and arecompared to existing data. When scaled by Z/A, the Q-dependence of all thefar-forward angle (theta < 10 degrees) data from $^{1}$H to $^{27}$Al can bedescribed by the same slope out to $Q \approx 0.35$ GeV. Larger-angle data fromother experiments in the same Q range are consistent with a slope about twiceas steep.

We report measurements of the parity-conserving beam-normal single-spinelastic scattering asymmetries $B_n$ on $^{12}$C and $^{27}$Al, obtained withan electron beam polarized transverse to its momentum direction. Thesemeasurements add an additional kinematic point to a series of previousmeasurements of $B_n$ on $^{12}$C and provide a first measurement on $^{27}$Al.The experiment utilized the Qweak apparatus at Jefferson Lab with a beam energyof 1.158 GeV. The average lab scattering angle for both targets was 7.7degrees, and the average $Q^2$ for both targets was 0.02437 GeV$^2$ (Q=0.1561GeV). The asymmetries are $B_n$ = -10.68 $\pm$ 0.90 stat) $\pm$ 0.57 (syst) ppmfor $^{12}$C and $B_n$ = -12.16 $\pm$ 0.58 (stat) $\pm$ 0.62 (syst) ppm for$^{27}$Al. The results are consistent with theoretical predictions, and arecompared to existing data. When scaled by Z/A, the Q-dependence of all thefar-forward angle (theta < 10 degrees) data from $^{1}$H to $^{27}$Al can bedescribed by the same slope out to $Q \approx 0.35$ GeV. Larger-angle data fromother experiments in the same Q range are consistent with a slope about twiceas steep.

We present new precision measurements of the elastic electron-protonscattering cross section for momentum transfer (Q$^2$) up to 15.75~\gevsq.Combined with existing data, these provide an improved extraction of the protonmagnetic form factor at high Q$^2$ and double the range over which alongitudinal/transverse separation of the cross section can be performed. Thedifference between our results and polarization data agrees with that observedat lower Q$^2$ and attributed to hard two-photon exchange (TPE) effects,extending to 8~(GeV/c)$^2$ the range of Q$^2$ for which a discrepancy isestablished at $>$95\% confidence. We use the discrepancy to quantify the sizeof TPE contributions needed to explain the cross section at high Q$^2$.

We report measurements of the exclusive neutral pion electroproduction crosssection off protons at large values of $x_B$ (0.36, 0.48 and 0.60) and $Q^2$(3.1 to 8.4 GeV$^2$) obtained from Jefferson Lab Hall A experiment E12-06-014.The corresponding structure functions $d\sigma_L/dt+\epsilon d\sigma_T/dt$,$d\sigma_{TT}/dt$, $d\sigma_{LT}/dt$ and $d\sigma_{LT'}/dt$ are extracted as afunction of the proton momentum transfer $t-t_{min}$. The results suggest theamplitude for transversely polarized virtual photons continues to dominate thecross-section throughout this kinematic range. The data are well described bycalculations based on transversity Generalized Parton Distributions coupled toa helicity flip Distribution Amplitude of the pion, thus providing a unique wayto probe the structure of the nucleon.

We report the first measurement of the parity-violating elastic electron scattering asymmetry on ^{27}Al. The ^{27}Al elastic asymmetry is A&#95;{PV}=2.16±0.11(stat)±0.16(syst)  ppm, and was measured at ⟨Q^{2}⟩=0.02357±0.00010  GeV^{2}, ⟨θ&#95;{lab}⟩=7.61°±0.02°, and ⟨E&#95;{lab}⟩=1.157  GeV with the Q&#95;{weak} apparatus at Jefferson Lab. Predictions using a simple Born approximation as well as more sophisticated distorted-wave calculations are in good agreement with this result. From this asymmetry the ^{27}Al neutron radius R&#95;{n}=2.89±0.12  fm was determined using a many-models correlation technique. The corresponding neutron skin thickness R&#95;{n}-R&#95;{p}=-0.04±0.12  fm is small, as expected for a light nucleus with a neutron excess of only 1. This result thus serves as a successful benchmark for electroweak determinations of neutron radii on heavier nuclei. A tree-level approach was used to extract the ^{27}Al weak radius R&#95;{w}=3.00±0.15  fm, and the weak skin thickness R&#95;{wk}-R&#95;{ch}=-0.04±0.15  fm. The weak form factor at this Q^{2} is F&#95;{wk}=0.39±0.04.

A beam-normal single-spin asymmetry generated in the scattering of transversely polarized electrons from unpolarized nucleons is an observable related to the imaginary part of the two-photon exchange process. We report a 2% precision measurement of the beam-normal single-spin asymmetry in elastic electron-proton scattering with a mean scattering angle of θ&#95;{lab}=7.9° and a mean energy of 1.149 GeV. The asymmetry result is B&#95;{n}=-5.194±0.067(stat)±0.082 (syst) ppm. This is the most precise measurement of this quantity available to date and therefore provides a stringent test of two-photon exchange models at far-forward scattering angles (θ&#95;{lab}→0) where they should be most reliable.

We present the annotation of the draft genome sequence of Oscheius sp. TEL-2014 (Genbank accession number KM492926). This entomopathogenic nematode was isolated from grassland in Suikerbosrand Nature Reserve near Johannesburg in South Africa. Oscheius sp. Strain TEL has a genome size of 110,599,558 bp and a GC content of 42.24%. The genome sequence can be accessed at DDBJ/EMBL/GenBank under the accession number LNBV00000000.

Here, we report the draft genome sequence of Photorhabdus heterorhabditis strain VMG, a symbiont of the entomopathogenic nematode Heterorhabditis zealandica in South Africa. The draft genome sequence is 4,878,919 bp long and contains 4,023 protein-coding genes. The genome assembly contains 262 contigs with a G+C content of 42.22%., (Copyright © 2015 Naidoo et al.)

Here, we describe the draft genome sequence of Xenorhabdus sp. GDc328, an endosymbiont of the native South African entomopathogenic nematode host, Steinernema khoisanae. The total genome size of the bacteria is 4.09 Mb. The genome comprises a total of 3,608 genes with a molecular G+C content of 44.64%., (Copyright © 2015 Soobramoney et al.)

We present the annotation of the draft genome sequence of Serratia sp. strain TEL (GenBank accession number KP711410). This organism was isolated from entomopathogenic nematode Oscheius sp. strain TEL (GenBank accession number KM492926) collected from grassland soil and has a genome size of 5,000,541 bp and 542 subsystems. The genome sequence can be accessed at DDBJ/EMBL/GenBank under the accession number LDEG00000000.

We report here the draft genome sequence of Xenorhabdus khoisanae strain MCB, a Gram-negative bacterium and symbiont of a Steinernema entomopathogenic nematode. The genome assembly consists of 266 contigs covering 4.68 Mb. Genome annotation revealed 3,869 protein-coding sequences, with a G+C content of 43.5%., (Copyright © 2015 Naidoo et al.)

Here, we report on the draft genome sequence of Serratia sp. strain TEL, associated with Oscheius sp. TEL-2014 (Nematoda: Rhabditidae, KM492926) isolated from a grassland in Suikerbosrand Nature Reserve near Johannesburg in South Africa. Serratia sp. strain TEL has a genome size of 5,000,541 bp with 4,647 genes and a G+C content of 59.1%., (Copyright © 2015 Lephoto et al.)

Here we report on the draft genome sequence of Serratia marcescens strain MCB associated with Oscheius sp. MCB (Nematoda: Rhabditidae) isolated from South African soil. S. marcescens strain MCB has 5,304,212-bp genome size with 4,877 genes and a G+C content of 59.1%., (Copyright © 2014 Serepa and Gray.)

The effect of varying levels of phosphorus (P) on Isochrysis galbana U4 growth, pigmentation and lipid accumulation were investigated. A reduction in the P content to 25% of the recommended level for f/2 medium did not lead to declines in cell growth rates or lipid accumulation levels relative to the cultures maintained on medium supplemented with the normal P dose. Evidence suggesting that the recommended P supply in f/2 exceeds the requirements for maximal algal growth has obvious economic implications for the mass production of I. galbana for biodiesel production. When P supply was in excess this species was also found to accumulate intracellular levels of P that exceeded by up to 6 times its P requirements for growth and cell division. The reduction in P concentration to levels below 25% resulted in P starvation stimulated chlorophyll reductions and carotenoid and lipid accumulation in this species., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

The Q(weak) experiment has measured the parity-violating asymmetry in ep elastic scattering at Q(2)=0.025(GeV/c)(2), employing 145 μA of 89% longitudinally polarized electrons on a 34.4 cm long liquid hydrogen target at Jefferson Lab. The results of the experiment's commissioning run, constituting approximately 4% of the data collected in the experiment, are reported here. From these initial results, the measured asymmetry is A(ep)=-279±35 (stat) ± 31 (syst) ppb, which is the smallest and most precise asymmetry ever measured in ep scattering. The small Q(2) of this experiment has made possible the first determination of the weak charge of the proton Q(W)(p) by incorporating earlier parity-violating electron scattering (PVES) data at higher Q(2) to constrain hadronic corrections. The value of Q(W)(p) obtained in this way is Q(W)(p)(PVES)=0.064±0.012, which is in good agreement with the standard model prediction of Q(W)(p)(SM)=0.0710±0.0007. When this result is further combined with the Cs atomic parity violation (APV) measurement, significant constraints on the weak charges of the up and down quarks can also be extracted. That PVES+APV analysis reveals the neutron's weak charge to be Q(W)(n)(PVES+APV)=-0.975±0.010.

Biohydrogen production in an anaerobic fluidized granular bed bioreactor was strongly dependent on temperature and effluent recycle rates. At 45 °C as the effluent recycle rate was increased from 1.3 to 3.5 L/min, the total H₂ output for the bioreactor increased from 10.6 to 43.2 L/h. Volumetric H(2) productivity also increased from 2.1 to 8.7 L H₂/L/h. At 70°C as the effluent recycle was increased from 1.3 to 3.5 L/min, the total H₂ output for the bioreactor increased from 13.8 to 73.8L/h. At 70 °C volumetric H(2) productivities increased from 2.8 to 14.8L H₂/L/h as the effluent recycle rate was increased from 1.3 to 3.5 L/min. At 45 °C % H₂ was 45% and reached 67% at 70 °C. Maximum hydrogen yields at 45 °C were 1.24 and 2.2 mol H₂/mol glucose at 70 °C., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

This study aimed to confirm the identity of three strains of the entomopathogenic fungus Beauveria bassiana from South African soils and to investigate their phylogenetic relationship with non-indigenous strains from other geographic regions. Sequences of the rDNA ITS1-5.8S-ITS2 region of 23 strains were compared with the Genbank reference sequences of 20 other cosmopolitan strains. Fitch parsimony and neighbor-joining analyses of the ITS1-5.8S-ITS2 regions resolved the strains into two distinct clades and matched them to four species groups/lineages: Beauveria bassiana, B. cf. bassiana (pseudobassiana), B. brongniartii and B. caledonica. Two of the South African strains initially identified as B. bassiana grouped with B. caledonica, whereas the third strain was confirmed as B. bassiana. Because of the paucity of Genbank references for B. caledonica, we have designated the two South African B. caledonica strains as B. sp. aff. caledonica. Other reassignments included two strains from Norway, originally classified as B. bassiana, being grouped with B. brongniartii, and three of the B. brongniartii reference taxa from Brazil which were clearly placed in the B. bassiana clade. The study provides a first report of the presence of the B. caledonica lineage in Africa and confirms current Beauveria phylogenies inferred from molecular data.

Increasingly lignocellulosic biomass hydrolysates are used as the feedstock for industrial fermentations. These biomass hydrolysates consist of complex mixtures of different fermentable sugars, but also contain inhibitors and salts that affect the performance of the product-generating microbes. The performance of six industrially relevant microorganisms, i.e., two bacteria (Escherichia coli and Corynebacterium glutamicum), two yeasts (Saccharomyces cerevisiae and Pichia stipitis) and two fungi (Aspergillus niger and Trichoderma reesei) were compared for their ability to utilize and grow on different feedstock hydrolysates (corn stover, wheat straw, sugar cane bagasse and willow wood). Moreover, the ability of the selected hosts to utilize waste glycerol from the biodiesel industry was evaluated. P. stipitis and A. niger were found to be the most versatile and C. glutamicum, and S. cerevisiae were shown to be the least adapted to renewable feedstocks. Clear differences in the utilization of the more abundant carbon sources in these feedstocks were observed between the different species. Moreover, in a species-specific way the production of various metabolites, in particular polyols, alcohols and organic acids was observed during fermentation. Based on the results obtained we conclude that a substrate-oriented instead of the more commonly used product oriented approach towards the selection of a microbial production host will avoid the requirement for extensive metabolic engineering. Instead of introducing multiple substrate utilization and detoxification routes to efficiently utilize lignocellulosic hydrolysates only one biosynthesis route forming the product of interest has to be engineered., (© 2010 Landes Bioscience)

Gram-negative bacteria with the potential to metabolize n-alkanes and cyclic hydrocarbons were isolated from local soils and identified using 16S rDNA sequence analysis. Three isolates (CS1CO, GL1CO, GCI1CO) were identified as strains of Pseudomonas (P.) aeruginosa and a further strain (DSS2) as P. putida. Isolates were co-cultured in a laboratory-scale fluidized bed biofilm bioreactor (FBBR) utilizing sodium benzoate as the sole carbon source, under two batch and/or one continuous growth conditions. Biofilm and planktonic bacterial growth dynamics were monitored by plate counts, and optical density measurements (230 nm) determined benzoate biodegradation. Overall higher attached and planktonic bacterial counts, and benzoate depletion, were determined under batch compared to continuous conditions, and the bioreactor performed better during the second batch phase when compared to the first batch phase. It thus appeared that both the planktonic and biofilm components of the system were necessary for the most successful sodium benzoate degradation in this system.

Carrier induced granular particles comprising Enterobacter cloacae and Citrobacter freundii were used to generate H(2) from sucrose in an anaerobic fluidized bed bioreactor. At a hydraulic retention time of 4.5 h, 95.8% of the sucrose was consumed and the rate of H(2) production reached 180 mmol H(2) l h(-1). Biogas composition for H(2) and CO(2) was 42 and 55%, respectively.

Background and Aims: The aim of this study was to investigate the effects of the interactions between the microbial symbionts, Rhizobium and arbuscular mycorrhizal fungi (AMF) on N and P accumulation by broad bean (Vicia faba) and how increased N and P content influence biomass production, leaf area and net photosynthetic rate., Methods: A multi-factorial experiment consisting of four different legume-microbial symbiotic associations and two nitrogen treatments was used to investigate the influence of the different microbial symbiotic associations on P accumulation, total N accumulation, biomass, leaf area and net photosynthesis in broad bean grown under low P conditions., Key Results: AMF promoted biomass production and photosynthetic rates by increasing the ratio of P to N accumulation. An increase in P was consistently associated with an increase in N accumulation and N productivity, expressed in terms of biomass and leaf area. Photosynthetic N use efficiency, irrespective of the inorganic source of N (e.g. NO3- or N2), was enhanced by increased P supply due to AMF. The presence of Rhizobium resulted in a significant decline in AMF colonization levels irrespective of N supply. Without Rhizobium, AMF colonization levels were higher in low N treatments. Presence or absence of AMF did not have a significant effect on nodule mass but high N with or without AMF led to a significant decline in nodule biomass. Plants with the Rhizobium and AMF symbiotic associations had higher photosynthetic rates per unit leaf area., Conclusions: The results indicated that the synergistic or additive interactions among the components of the tripartite symbiotic association (Rhizobium-AMF-broad bean) increased plant productivity.

Culture of cassava somatic embryos on media with an altered macro- and micro-nutrient salt concentration affected embryo development and germination capability. In the tests, quarter-, half-, full- or double-strength Murashige and Skoog (MS) media were compared. The maximum number of somatic embryos differentiated from a proliferative nodular embryogenic callus (NEC) on either half- or full-strength MS medium, and the greatest numbers of cotyledonary stage embryos were formed on full-strength MS medium. Developed somatic embryos were then desiccated above a saturated K2SO4 solution for 10 d. After transfer to germination medium, embryos that had developed on half- and full-strength MS medium yielded 8.3 and 8.6 germinants g(-1) NEC tissue, respectively. For this important but often disregarded culture factor, either half- or full-strength MS medium is recommended for both the differentiation and development of cassava somatic embryos that are capable of germination.

The rate of in-vivo nitrate reduction by leaf segments of Zea mays L. was found to decline during the second hour of dark anaerobic treatment. On transfer to oxygen the capacity to reduce nitrate under dark conditions was restored. These observations led to the proposal that nitrate reductase is a regulatory enzyme with ADP acting as a negative effector. The effect of ADP on the invitro activity of nitrate reductase and the changes in the in-vivo adenylate pool under dark-N2 and dark-O2 were investigated. It was found that ADP inhibited the activity of partially purified nitrate reductase. Similarly, the in-vivo anaerobic inhibition of nitrate reduction was associated with a build-up of ADP in the leaf tissue. Under anaerobic conditions nitrite accumulated and on transfer to oxygen the accumulated nitrite was reduced. To explain this phenomenon the following hypothesis was proposed and tested. Under anaerobic conditions the supply of reducing equivalents for nitrite reduction in the plastid becomes restricted and nitrite accumulates as a consequence. On transfer to oxygen this restriction is removed and nitrite disappears. This capacity to reduce accumulated nitrite was found to be dependent on the carbohydrate status of the leaf tissue.

The assimilation of nitrate under dark-N2 and dark-O2 conditions in Zea mays leaf tissue was investigated using colourimetric and (15)N techniques for the determination of organic and inorganic nitrogen. Studies using (15)N indicated that nitrate was assimilated under dark conditions. However, the rate of nitrate assimilation in the dark was only 28% of the rate under non-saturating light conditions. No nitrite accumulated under dark aerobiosis, even though nitrate reduction occurred under these conditions. The pattern of nitrite accumulation in leaf tissue in response to dark-N2 conditions consisted of three phases: an initial lag phase, followed by a period of rapid nitrite accumulation and finally a phase during which the rate of nitrite accumulation declined. After a 1-h period of dark-anaerobiosis, both nitrate reduction and nitrite accumulation declined considerably. However, when O2 was supplied, nitrate reduction was stimulated and the accumulated nitrite was rapidly reduced. Anaerobic conditions stimulated nitrate reduction in leaf tissue after a period of dark-aerobic pretreatment.