bluuebunny/crossref_metadata_2025 huggingface dataset:
Thickness-independent memory effect in ferroelectric liquid crystals
Authors: Kaur S. , Thakur A. K. , Bawa S. S. , Biradar A. M.
Published: March 2006

Memory in ferroelectric liquid crystals (FLCs) is well known in the literature where thickness of the cell is less than the pitch value of the material. Here, we report a thickness independent memory in a class of FLCs called the de Vries electroclinic liquid crystals. Thickness independency of memory effect is observed by dielectric spectroscopy and texture observation. The memory observed in SmC* phase of de Vries material is entirely different from conventional FLCs. In the former case, it is the inherent property of the material but in the latter it is dependent on the cell geometry. In de Vries material, it is probably the randomization that is playing a major role.
Pd
30
Pt
17.5
Cu
32.5
P
20
alloy with low critical cooling rate of 0.067K∕s
Authors: Nishiyama N. , Takenaka K. , Inoue A.
Published: March 2006

In order to realize biomedical applications of bulk glassy alloys, Pd-based glassy alloys with Ni-free composition were developed. The alloy with the highest glass-forming ability was obtained at a composition of Pd30Pt17.5Cu32.5P20. The critical cooling rate for glass formation was measured to be 0.050–0.067K∕s. It is also recognized that the crystallization of the undercooled alloy is mainly dominated by surface nucleation. The apparent crystal growth rate of the alloy was slightly higher than that of the previously reported Pd40Cu30Ni10P20 alloy at the same degree of undercooling. The highly processable feature of the alloy has potential for biomedical applications.
Deep-ultraviolet Al0.75Ga0.25N photodiodes with low cutoff wavelength
Authors: Butun Serkan , Tut Turgut , Butun Bayram , Gokkavas Mutlu , Yu HongBo , Ozbay Ekmel
Published: March 2006

Deep ultraviolet Al0.75Ga0.25N metal-semiconductor-metal photodetectors with high Al concentration have been demonstrated. A metal-organic chemical vapor deposition grown high quality Al0.75Ga0.25N layer was used as a template. Spectral responsivity, current-voltage, optical transmission, and noise measurements were carried out. The photodetectors exhibited a 229nm cutoff wavelength and a peak responsivity of 0.53A∕W at 222nm. Some 100×100μm2 devices have shown a dark current density of 5.79×10−10A∕cm2 under 50V bias. An ultraviolet-visible rejection ratio of seven orders of magnitude was obtained from the fabricated devices.
Nanoparticle-induced negative differential resistance and memory effect in polymer bistable light-emitting device
Authors: Tseng Ricky J. , Ouyang Jianyong , Chu Chih-Wei , Huang Jinsong , Yang Yang
Published: March 2006

Recently, electrical bistability was demonstrated in polymer thin films incorporated with metal nanoparticles [J. Ouyang, C. W. Chu, C. R. Szmanda, L. P. Ma, and Y. Yang, Nat. Mater. 3, 918 (2004)]. In this letter, we show the evidence that electrons are the dominant charge carriers in these bistable devices. Direct integration of bistable polymer layer with a light-emitting polymer layer shows a unique light-emitting property modulated by the electrical bistability. A unique negative differential resistance induced by the charged gold nanoparticles is observed due to the charge trapping effect from the nanoparticles when interfaced with the light-emitting layer.
High-resolution imaging of electrochemical doping and dedoping processes in luminescent conjugated polymers
Authors: Hu Yufeng , Tracy Corey , Gao Jun
Published: March 2006

We report fluorescence imaging of extremely large planar polymer light-emitting electrochemical cells (LECs) with high spatial and temporal resolution. The type of cation used has been shown to strongly affect n-doping propagation. When left to relax, p doping undergoes significantly faster relaxation than n doping. Imaging also confirms that a p-n junction, rather than a p-i-n junction, is formed in fully turned on LECs, which suffer from heavy photoluminescence quenching throughout the polymer film. However, a p-i-n junction with a much less quenched “intrinsic” region can be formed by relaxing a p-n junction without bias, suggesting a simple approach for achieving more efficient LECs.
Optical power degradation mechanisms in AlGaN-based 280nm deep ultraviolet light-emitting diodes on sapphire
Authors: Gong Z. , Gaevski M. , Adivarahan V. , Sun W. , Shatalov M. , Asif Khan M.
Published: March 2006

We present a study of reliability of AlGaN-based 280nm deep ultraviolet light-emitting diodes on sapphire substrate grown by migration-enhanced metal-organic chemical vapor deposition. Two modes of optical power degradation were observed: catastrophic and gradual. The catastrophic degradation is believed to be due to metal alloying at macroscopic defects in the top p layers of the light-emitting diode structure. For the gradual power degradation, two time constants were determined, which were temperature and bias dependent. For the temperature-dependent part, the values of the activation energies and room-temperature degradation rates at dc currents of 10 and 20mA were determined to be 0.23 and 0.27eV and 1.31×10−3and5.93×10−3h−1, respectively.
Low-temperature-sensitivity heterostructure photonic-crystal wavelength-selective filter based on ultralow-refractive-index metamaterials
Authors: Ioannou Florous Nikolaos , Saitoh Kunimasa , Koshiba Masanori , Skorobogatiy Maksim
Published: March 2006

We propose and numerically investigate the thermal-insensitive properties of a wavelength-selective filter based on heterostructure photonic crystals with ultralow-refractive-index metallic nanowires. The operational principle of the proposed device is based on the photon trapping by total external reflections between the ultralow refractive index metamaterial claddings and the guiding air cores. The low propagation losses, the ultracompact size as well as the temperature-insensitive operation are the main advantages of the proposed metamaterial technology, making the proposed de-multiplexer an excellent candidate for applications in nanophotonic-integrated systems operating in the visible frequency spectrum.
High-performance ZnO thin-film transistors on gate dielectrics grown by atomic layer deposition
Authors: Carcia P. F. , McLean R. S. , Reilly M. H.
Published: March 2006

We fabricated high-performance ZnO thin-film transistors on gate dielectrics of HfO2, HfSiOx, and Al2O3, grown by atomic layer deposition (ALD). Devices on HfO2 had a mobility of 12.2cm2∕Vs with a threshold voltage of 2.6V and subthreshold slope of 0.5V∕decade. Device performance on Al2O3 depended on synthesis temperature. For 100nm thick Al2O3, synthesized at 200°C, ZnO devices had a mobility of 17.6cm2∕Vs with a threshold voltage of 6V and less than ∼0.1nA gate leakage at 20V. The overall trends were that devices on Hf oxides had a lower threshold voltage, while the gate leakage current density was lower on Al2O3. Device characteristics for all ALD dielectrics exhibited negligibly small hysteresis, suggesting a low defect density at the interface of ZnO with the gate dielectric.
Taxonomic and phylogenetic revision of the Gelastocephalini (Hemiptera:Cixiidae)
Authors: Löcker Birgit , Fletcher Murray J. , Larivière Marie-Claude , Gurr Geoff M. , Holzinger Werner E. , Löcker Holger
Published: March 2006

Planthoppers of the family Cixiidae Spinola, 1839 are economically important owing to their ability to transmit phytoplasmas causing yellows-type diseases. The tribe Gelastocephalini Emeljanov, one of 16 tribes within the subfamily Cixiinae, has never been revised comprehensively. Twenty new genera (Aubirestus, Balyadimetopia, Barbonia, Candicarina, Corylonga, Fletcherolus, Gelastocaledonia, Gurrundus, Guttala, Hartliebia, Holgus, Larivierea, Lipsia, Melanoclypeus, Novotarberus, Payastylus, Rokebia, Schuerrera, Wernindia, Yarnikada) and 50 new species (Aubirestus semicirculatus, Balyadimetopia frederi, B. krahalla, B. marci, Barbonia spectabilis, Candicarina geroldi, C. pulchra, Carolus carinatus, C. stiriae, Corylonga aaroni, C. krottendorfi, C. leighi, C. lobata, C. loisae, C. mahmudae, C. triangula, Fletcherolus lanceolatus, F. monospinosus, Gelastocaledonia monteithi, Gelastocephalus velifer, Gurrundus fuscomarginatus, G. nectostylus, Guttala bernhardtae, G. mona, G. nickeli, G. robierae, Hartliebia towinna, Holgus ancistrus, H. liafredis, H. spiralis, H. unispinosus, Larivierea yalthi, L. yokunna, Lipsia mystrostylus, Melanoclypeus cristatus, M. uncinatus, Novotarberus flagellospinosus, N. pseudorphninus, N. remanei, Payastylus brichrius, P. gekiae, P. kernae, Rokebia australis, Ronaldia emeljanovi, Schuerrera clypeocarinata, S. ecarinata, ,Wernindia bubalis, W. lorda, W. rhomboidea, Yarnikada ulliae) are described. This increases the number of known Gelastocephalini from seven to 27 genera and from nine to 60 species. A new combination, Novotarberus jacobii, is proposed for Gelastocephalus jacobii from New Caldedonia and Cixius merula was transferred into the genus Schuerrera, resulting in a new combination, Schuerrera merula. A preliminary cladistic analysis of morphological data including all species of Gelastocephalini supported the monophyly of the tribe and its genera. The short male anal style is recognised as a synapomorphy for the tribe. The subtribe Rhigedanina was shown to be monophyletic whereas Gelastocephalina is paraphyletic. Three alternative hypotheses are presented to explain the current distribution of the tribe, which is restricted to Australia and New Caledonia. The species Novotarberus jacobii and Gelastocaledonia monteithi seem to be Gondwanan relicts.
Kapu (Diptera:Bombyliidae:Anthracinae:Exoprosopini), a replacement name for the Australian genus Kapua Lambkin & Yeates
Authors: Lambkin Christine L. , Yeates David K.
Published: March 2006

The replacement name Kapu is provided for the Australian beefly genus Kapua Lambkin & Yeates (Bombyliidae : Anthracinae : Exoprosopini). Kapua Lambkin & Yeates is a junior homonym of the molluscan fossil Kapua Marwick (Gastropoda : Sorbeoconcha : Janthinoidea : Epitoniidae).
Downstream boundary of chromosomal R-loops at murine switch regions: Implications for the mechanism of class switch recombination
Authors: Huang Feng-Ting , Yu Kefei , Hsieh Chih-Lin , Lieber Michael R.
Published: March 2006

R-loops form at Sγ3 and Sγ2b Ig class switch regions in the chromosomes of stimulated murine primary B cells and are suspected to be a general feature of mammalian class switch regions. The
in vivo
upstream boundary of the R-loops is known to begin within the switch repeats. To determine how precisely the R-loop structure conforms to the repetitive zone of the murine Sγ3 and Sγ2b switch regions, a chemical probing method was used to obtain structural information on the downstream boundary. We find that only 61–67% of the R-loops terminate within the Sγ3 and the Sγ2b repetitive zones, and the remainder terminate downstream, usually within the first 600 bp immediately downstream of the core switch repeats. Interestingly, the nontemplate strand G density falls to the random level gradually through this same region. Hence, the R-loops terminate as the G-richness of the nascent RNA strand falls. This finding is consistent with thermodynamic predictions for RNA:DNA duplex strength relative to that of DNA:DNA duplexes. This result contrasts with the location of known recombination breakpoints, which correlate not with G-richness and R-loop location but rather with AGCT density. The implications of these findings are discussed in the context of models for the targeting of class switch recombination.
Essential role for hematopoietic prostaglandin D2 synthase in the control of delayed type hypersensitivity
Authors: Trivedi Seema G. , Newson Justine , Rajakariar Ravindra , Jacques Thomas S. , Hannon Robert , Kanaoka Yoshihide , Eguchi Naomi , Colville-Nash Paul , Gilroy Derek W.
Published: March 2006

Hematopoietic prostaglandin D2synthase (hPGD2S) metabolizes cyclooxygenase-derived prostaglandin (PG) H2to PGD2, which is dehydrated to cyclopentenone PGs, including 15-deoxy-Δ12,14-PGJ2(15d-PGJ2). PGD2acts through two receptors (DP1 and DP2/CRTH2), whereas 15d-PGJ2can activate peroxisome proliferator-activated receptors or inhibit a range of proinflammatory signaling pathways, including NF-κB. Despite eliciting asthmatic and allergic reactions through the generation of PGD2, it is not known what role hPGD2S plays in T helper (Th)1-driven adaptive immunity. To investigate this question, the severity and duration of a delayed type hypersensitivity reaction was examined in hPGD2S knockout and transgenic mice. Compared with their respective controls, knockouts displayed a more severe inflammatory response that failed to resolve, characterized histologically as persistent acute inflammation, whereas transgenic mice had little detectable inflammation. Lymphocytes isolated from inguinal lymph nodes ofhPGD2S−/−animals showed hyperproliferation and increased IL-2 synthesis effects that were rescued by 15d-PGJ2, but not PGD2, working through either of its receptors. Crucially, 15d-PGJ2exerted its suppressive effects through the inhibition of NF-κB activation and not through peroxisome proliferator-activated receptor signaling. In contrast, lymph node cultures from transgenics proliferated more slowly and synthesized significantly less IL-2 than controls. Therefore, contrary to its role in driving Th2-like responses, this report shows that hPGD2S may act as an internal braking signal essential for bringing about the resolution of Th1-driven delayed type hypersensitivity reactions. Consequently, hPGD2S-derived cyclopentenone PGs may protect against inflammatory diseases, where T lymphocytes play a pathogenic role, as in rheumatoid arthritis, atopic eczema, and chronic rejection.
Ab-induced ectodomain shedding mediates hepatocyte growth factor receptor down-regulation and hampers biological activity
Authors: Petrelli Annalisa , Circosta Paola , Granziero Luisa , Mazzone Massimiliano , Pisacane Alberto , Fenoglio Silvia , Comoglio Paolo M. , Giordano Silvia
Published: March 2006

Targeting tyrosine kinase receptors (RTKs) with specific Abs is a promising therapeutic approach for cancer treatment, although the molecular mechanism(s) responsible for the Abs’ biological activity are not completely known. We targeted the transmembrane RTK for hepatocyte growth factor (HGF) with a monoclonal Ab (DN30).
In vitro
, chronic treatment of carcinoma cell lines resulted in impairment of HGF-induced signal transduction, anchorage-independent growth, and invasiveness.
In vivo
, administration of DN30 inhibited growth and metastatic spread to the lung of neoplastic cells s.c. transplanted into immunodeficient
nu
/
nu
mice. This Ab efficiently down-regulates HGF receptor through a molecular mechanism involving a double proteolytic cleavage: (
i
) cleavage of the extracellular portion, resulting in “shedding” of the ectodomain, and (
ii
) cleavage of the intracellular domain, which is rapidly degraded by the proteasome. Interestingly, the “decoy effect” generated by the shed ectodomain, acting as a dominant negative molecule, enhanced the inhibitory effect of the Ab.
A role for direct interactions in the modulation of rhodopsin by ω-3 polyunsaturated lipids
Authors: Grossfield Alan , Feller Scott E. , Pitman Michael C.
Published: March 2006

Rhodopsin, the G protein-coupled receptor primarily responsible for sensing light, is found in an environment rich in polyunsaturated lipid chains and cholesterol. Biophysical experiments have shown that lipid unsaturation and cholesterol both have significant effects on rhodopsin’s stability and function; ω-3 polyunsaturated chains, such as docosahexaenoic acid (DHA), destabilize rhodopsin and enhance the kinetics of the photocycle, whereas cholesterol has the opposite effect. Here, we use molecular dynamics simulations to investigate the possibility that polyunsaturated chains modulate rhodopsin stability and kinetics via specific direct interactions. By analyzing the results of 26 independent 100-ns simulations of dark-adapted rhodopsin, we found that DHA routinely forms tight associations with the protein in a small number of specific locations qualitatively different from the nonspecific interactions made by saturated chains and cholesterol. Furthermore, the presence of tightly packed DHA molecules tends to weaken the interhelical packing. These results are consistent with recent NMR work, which proposes that rhodopsin binds DHA, and they suggest a molecular rationale for DHA’s effects on rhodopsin stability and kinetics.
CD4+regulatory T cell responses induced by T cell vaccination in patients with multiple sclerosis
Authors: Hong Jian , Zang Ying C. Q. , Nie Hong , Zhang Jingwu Z.
Published: March 2006

Immunization with irradiated autologous T cells (T cell vaccination) is shown to induce regulatory T cell responses that are poorly understood. In this study, CD4+regulatory T cell lines were generated from patients with multiple sclerosis that received immunization with irradiated autologous myelin basic protein-reactive T cells. The resulting CD4+regulatory T cell lines had marked inhibition on autologous myelin basic protein-reactive T cells and displayed two distinctive patterns distinguishable by the expression of transcription factor Foxp3 and cytokine profile. The majority of the T cell lines had high Foxp3 expression and secreted both IFN-γ and IL-10 as compared with the other pattern characteristic of low Foxp3 expression and predominant production of IL-10 but not IFN-γ. CD4+regulatory T cell lines of both patterns expressed CD25 and reacted with activated autologous T cells but not resting T cells, irrespective of antigen specificity of the target T cells. It was evident that they recognized preferentially a synthetic peptide corresponding to residues 61–73 of the IL-2 receptor α chain. T cell vaccination correlated with increased Foxp3 expression and T cell reactivity to peptide 61–73. The findings have important implications in the understanding of the role of CD4+regulatory T cell response induced by T cell vaccination.
Extended subnanosecond structural dynamics of myoglobin revealed by Laue crystallography
Authors: Bourgeois Dominique , Vallone Beatrice , Arcovito Alessandro , Sciara Giuliano , Schotte Friedrich , Anfinrud Philip A. , Brunori Maurizio
Published: March 2006

Work carried out over the last 30 years unveiled the role of structural dynamics in controlling protein function. Cavity networks modulate structural dynamics trajectories and are functionally relevant; in globins they have been assigned a role in ligand migration and docking. These findings raised renewed interest for time-resolved structural investigations of myoglobin (Mb), a simple heme protein displaying a photosensitive iron-ligand bond. Photodissociation of MbCO generates a nonequilibrium population of protein structures relaxing over a time range extending from picoseconds to milliseconds. This process triggers ligand migration to matrix cavities with clear-cut effects on the rate and yield of geminate rebinding. Here, we report subnanosecond time-resolved Laue diffraction data on the triple mutant YQR-Mb [Leu-29(B10)Tyr, His-64(E7)Gln, Thr-67(E10)Arg] that depict the sequence of structural events associated with heme and protein relaxation from 100 ps to 316 ns and above. The photodissociated ligand rapidly (<0.1 ns) populates the Xe-binding cavity distal to the heme. Moreover, the heme relaxation toward the deoxy configuration is heterogeneous, with a slower phase (≈ns) evident in these experiments. Damping of the heme response appears to result from a strain exerted by the E-helix via the CD-turn; Phe-43(CD1), in close contact with heme, opposes tilt until the strain is relieved. A comparison with crystallographic data on wild-type Mb and mutants Leu(
29
)Phe or Leu(
29
)Trp suggests that the internal structure controls the rate and amplitude of the relaxation events. A correlation between structural dynamics as unveiled by Laue crystallography and functional properties of Mb is presented.
Anl-RNA-based aquaretic agent that inhibits vasopressininvivo
Authors: Purschke Werner G. , Eulberg Dirk , Buchner Klaus , Vonhoff Stefan , Klussmann Sven
Published: March 2006

A class of diuretic/aquaretic agents based on mirror-image oligonucleotides (so-called Spiegelmers) has been identified. These molecules directly bind and inhibit the neuropeptide vasopressin (AVP). AVP is the major regulatory component of body fluid homeostasis mediated through binding to the renal V2receptor. Elevated plasma levels of AVP are implicated in several pathological conditions, mainly cardiovascular diseases. In congestive heart failure, AVP is part of a neuroendocrine imbalance that is responsible for progressive worsening of the disease. Employingin vitroselection techniques, RNA aptamers that bind to the unnaturald-configuration of AVP were isolated. The best aptamer displayed an affinity tod-AVP of ≈560 pM at 37°C. The corresponding Spiegelmer, a 38-mer mirror-image oligonucleotide (l-RNA) termed NOX-F37, inhibits vasopressin-dependent activation of V1aas well as V2receptors with IC50values of 6.1 nM and 1 nM, respectively. NOX-F37 administered to healthy rats effectively neutralized AVP and increased diuresis dose-dependently for 24 h. The mode of action was strictly aquaretic, i.e., the increase in urine volume was not accompanied by an increase in electrolytes. These results clearly prove thein vivoefficacy of NOX-F37 and points out its potential as a drug in the treatment of diseases that are associated with body fluid overload.
Structure of the MTIP–MyoA complex, a key component of the malaria parasite invasion motor
Authors: Bosch Jürgen , Turley Stewart , Daly Thomas M. , Bogh Stephen M. , Villasmil Michelle L. , Roach Claudia , Zhou Na , Morrisey Joanne M. , Vaidya Akhil B. , Bergman Lawrence W. , Hol Wim G. J.
Published: March 2006

The causative agents of malaria have developed a sophisticated machinery for entering multiple cell types in the human and insect hosts. In this machinery, a critical interaction occurs between the unusual myosin motor MyoA and the MyoA-tail Interacting Protein (MTIP). Here we present one crystal structure that shows three different conformations of
Plasmodium
MTIP, one of these in complex with the MyoA-tail, which reveal major conformational changes in the C-terminal domain of MTIP upon binding the MyoA-tail helix, thereby creating several hydrophobic pockets in MTIP that are the recipients of key hydrophobic side chains of MyoA. Because we also show that the MyoA helix is able to block parasite growth, this provides avenues for designing antimalarials.
Ionic contrast terahertz near-field imaging of axonal water fluxes
Authors: Masson Jean-Baptiste , Sauviat Martin-Pierre , Martin Jean-Louis , Gallot Guilhem
Published: March 2006

We demonstrate the direct and noninvasive imaging of functional neurons by ionic contrast terahertz near-field microscopy. This technique provides quantitative measurements of ionic concentrations in both the intracellular and extracellular compartments and opens the way to direct noninvasive imaging of neurons during electrical, toxin, or thermal stresses. Furthermore, neuronal activity results from both a precise control of transient variations in ionic conductances and a much less studied water exchange between the extracellular matrix and the intraaxonal compartment. The developed ionic contrast terahertz microscopy technique associated with a full three-dimensional simulation of the axon-aperture near-field system allows a precise measurement of the axon geometry and therefore the direct visualization of neuron swelling induced by temperature change or neurotoxin poisoning. Water influx as small as 20 fl per μm of axonal length can be measured. This technique should then provide grounds for the development of advanced functional neuroimaging methods based on diffusion anisotropy of water molecules.
Autophagic programmed cell death by selective catalase degradation
Authors: Yu Li , Wan Fengyi , Dutta Sudeshna , Welsh Sarah , Liu ZhiHua , Freundt Eric , Baehrecke Eric H. , Lenardo Michael
Published: March 2006

Autophagy plays a central role in regulating important cellular functions such as cell survival during starvation and control of infectious pathogens. Recently, it has been shown that autophagy can induce cells to die; however, the mechanism of the autophagic cell death program is unclear. We now show that caspase inhibition leading to cell death by means of autophagy involves reactive oxygen species (ROS) accumulation, membrane lipid oxidation, and loss of plasma membrane integrity. Inhibition of autophagy by chemical compounds or knocking down the expression of key autophagy proteins such as ATG7, ATG8, and receptor interacting protein (RIP) blocks ROS accumulation and cell death. The cause of abnormal ROS accumulation is the selective autophagic degradation of the major enzymatic ROS scavenger, catalase. Caspase inhibition directly induces catalase degradation and ROS accumulation, which can be blocked by autophagy inhibitors. These findings unveil a molecular mechanism for the role of autophagy in cell death and provide insight into the complex relationship between ROS and nonapoptotic programmed cell death.
Chx10 is required to block photoreceptor differentiation but is dispensable for progenitor proliferation in the postnatal retina
Authors: Livne-bar Izzy , Pacal Marek , Cheung Melissa C. , Hankin Mark , Trogadis Judy , Chen Danian , Dorval Kimberley M. , Bremner Rod
Published: March 2006

In the
Chx10
-null ocular retardation (or
J
) mouse, retinal progenitor cell (RPC) proliferation is impaired, and bipolar neurons, a late born cell type, fail to differentiate. It is unclear whether
Chx10
is required to maintain proliferation throughout retinogenesis or whether the bipolar cell defect is an indirect effect of growth arrest. We show that
Chx10
is dispensable for late-stage RPC proliferation but is essential to promote bipolar cell genesis in place of rods. Ectopic
Chx10
expression drove bipolar instead of rod cell differentiation without affecting division. Converting
Chx10
to an activator impaired bipolar cell differentiation, implying that repression is important for
Chx10
activity. In the
Chx10
null or
J
retina, only a small fraction of cells expressing mutated
Chx10
mRNA were rods, but this fraction increased after

p27
Kip1

inactivation, which partially rescues proliferation. Most significantly, acute
Chx10
knockdown in the postnatal retina promoted rods in place of bipolar neurons without affecting division. Thus,
Chx10
directly controls bipolar cell genesis by inhibiting rod differentiation independent of its temporally limited early effect on RPC proliferation.
Differential interaction of spin-labeled arrestin with inactive and active phosphorhodopsin
Authors: Hanson Susan M. , Francis Derek J. , Vishnivetskiy Sergey A. , Kolobova Elena A. , Hubbell Wayne L. , Klug Candice S. , Gurevich Vsevolod V.
Published: March 2006

Arrestins regulate signaling and trafficking of G protein-coupled receptors by virtue of their preferential binding to the phosphorylated active form of the receptor. To identify sites in arrestin involved in receptor interaction, a nitroxide-containing side chain was introduced at each of 28 different positions in visual arrestin, and the dynamics of the side chain was used to monitor arrestin interaction with phosphorylated forms of its cognate receptor, rhodopsin. At physiological concentrations, visual arrestin associates with both inactive dark phosphorylated rhodopsin (P-Rh) and light-activated phosphorylated rhodopsin (P-Rh*). Residues distributed over the concave surfaces of the two arrestin domains are involved in weak interactions with both states of phosphorhodopsin, and the flexible C-terminal sequence (C-tail) of arrestin becomes dynamically disordered in both complexes. A large-scale movement of the C-tail is demonstrated by direct distance measurements using a doubly labeled arrestin with one nitroxide in the C-tail and the other in the N-domain. Despite some overlap, the molecular “footprint” of arrestin bound to P-Rh and P-Rh* is different, showing the structure of the complexes to be unique. Strong immobilizing interactions with residues in a highly flexible loop between β-strands V and VI are only observed in complex with the activated state. This result identifies this loop as a key recognition site in the arrestin-P-Rh* complex and supports the view that flexible sequences are key elements in protein–protein interactions.
Improved performance of quantum cascade lasers through a scalable, manufacturable epitaxial-side-down mounting process
Authors: Tsekoun Alexei , Go Rowel , Pushkarsky Michael , Razeghi Manijeh , Patel C. Kumar N.
Published: March 2006

We report substantially improved performance of high-power quantum cascade lasers (QCLs) by using epitaxial-side-down mounting that provides superior heat dissipation properties. We used aluminum nitride as the heatsink material and gold–tin eutectic solder. We have obtained continuous wave power output of 450 mW at 20°C from mid-IR QCLs. The improved thermal management achieved with epitaxial-side-down mounting combined with a highly manufacturable and scalable assembly process should permit incorporation of mid-IR QCLs in reliable instrumentation.
Eukaryotic control on bacterial cell cycle and differentiation in the
Rhizobium
–legume symbiosis
Authors: Mergaert Peter , Uchiumi Toshiki , Alunni Benoît , Evanno Gwénaëlle , Cheron Angélique , Catrice Olivier , Mausset Anne-Elisabeth , Barloy-Hubler Frédérique , Galibert Francis , Kondorosi Adam , Kondorosi Eva
Published: March 2006

Symbiosis between legumes and
Rhizobium
bacteria leads to the formation of root nodules where bacteria in the infected plant cells are converted into nitrogen-fixing bacteroids. Nodules with a persistent meristem are indeterminate, whereas nodules without meristem are determinate. The symbiotic plant cells in both nodule types are polyploid because of several cycles of endoreduplication (genome replication without mitosis and cytokinesis) and grow consequently to extreme sizes. Here we demonstrate that differentiation of bacteroids in indeterminate nodules of
Medicago
and related legumes from the galegoid clade shows remarkable similarity to host cell differentiation. During bacteroid maturation, repeated DNA replication without cytokinesis results in extensive amplification of the entire bacterial genome and elongation of bacteria. This finding reveals a positive correlation in prokaryotes between DNA content and cell size, similar to that in eukaryotes. These polyploid bacteroids are metabolically functional but display increased membrane permeability and are nonviable, because they lose their ability to resume growth. In contrast, bacteroids in determinate nodules of the nongalegoid legumes lotus and bean are comparable to free-living bacteria in their genomic DNA content, cell size, and viability. Using recombinant
Rhizobium
strains nodulating both legume types, we show that bacteroid differentiation is controlled by the host plant. Plant factors present in nodules of galegoid legumes but absent from nodules of nongalegoid legumes block bacterial cell division and trigger endoreduplication cycles, thereby forcing the endosymbionts toward a terminally differentiated state. Hence,
Medicago
and related legumes have evolved a mechanism to dominate the symbiosis.
The effect of sward surface height on the response to mixed grazing by cattle and sheep
Authors: Wright I. A. , Jones J. R. , Davies D. A. , Davidson G. R. , Vale J. E.
Published: March 2006

An experiment was conducted to examine the effects of mixed grazing of sheep plus cattle under continuous stocking of permanent pasture at different sward heights. The experiment had a 2×3 factorial design, with two sward surface heights (4–5 and 8–10 cm) and three combinations of animal species viz., sheep only, cattle only and sheep plus cattle. There were two replicate plots of each treatment combination and the experiment was conducted over 2 years consecutively. The sheep were Beulah Speckled Face ewes and their single Suffolk-cross lambs while the cattle were yearling Charolais-cross steers. Six ‘core’ steers and six ‘core’ ewes and their lambs grazed plots, as appropriately, while additional, non-experimental steers and ewes and their lambs were used to maintain sward heights. Each year the steers and the ewes grazed the pastures from May to October, while lambs were weaned and removed each year from the experiment in July. There was no significant effect of mixed grazing on live-weight gain of steers, but ewes had significantly higher live-weight gains on the sheep plus cattle treatment than on the sheep-only treatment (82 v. 61 g/day;P<0·001). The live-weight gain of the lambs was higher on the mixed grazing treatment than on the sheep only treatment on the 8–10 cm sward height treatment (243 v. 212 g/day;P<0·05) but there was no significant difference on the 4–5 cm sward height treatment (260 v. 250 g/day;P>0·05). The total output of live-weight gain per ha from steers, ewes and lambs was not significantly affected by animal species combination. It is concluded that while output per ha is not enhanced by mixed grazing by sheep and cattle when sward height is controlled, the live-weight gain of ewes is increased and the live-weight gain of lambs can be increased on taller swards.
Genetic analyses of carcass composition, as assessed by X-ray computer tomography, and meat quality traits in Scottish Blackface sheep
Authors: Karamichou E. , Richardson R. I. , Nute G. R. , McLean K. A. , Bishop S. C.
Published: March 2006

Genetic parameters for carcass composition and meat quality traits were estimated in Scottish Blackface sheep, previously divergently selected for carcass lean content (LEAN and FAT lines). Computerized X-ray tomography (CT) was used to obtain non-destructivein vivoestimates of the carcass composition of 700 lambs, at ca. 24 weeks of age, with tissue areas and image densities obtained for fat, muscle and bone components of the carcass. Comprehensive measures of meat quality and carcass fatness were made on 350 male lambs, at ca. 8 months of age, which had previously been CT scanned. Meat quality traits included intramuscular fat content, initial and final pH of the meat, colour attributes, shear force, dry matter, moisture and nitrogen proportions, and taste panel assessments of the cooked meat. FAT line animals were significantly (P<0·05) fatter than the LEAN line animals in all measures of fatness (from CT and slaughter data), although the differences were modest and generally proportionately less than 0·1. Correspondingly, the LEAN line animals were superior to the FAT line animals in muscling measurements. Compared with the LEAN line, the FAT line had lower muscle density (as indicated by the relative darkness of the scan image), greater estimated subcutaneous fat (predicted from fat classification score) at slaughter, more intramuscular fat content, a more ‘yellow’ as opposed to ‘red’ muscle colour, and juicer meat (allP<0·05). All CT tissue areas were moderately to highly heritable, with h2values ranging from 0·23 to 0·76. Likewise, meat quality traits were also moderately heritable. Muscle density was the CT trait most consistently related to meat quality traits, and genetic correlations of muscle density with live weight, fat class, subcutaneous fat score, dry matter proportion, juiciness, flavour and overall liking were all moderately to strongly negative, and significantly different from zero. In addition, intramuscular fat content was positively genetically correlated with juiciness and flavour, and negatively genetically correlated with shear force value. The results of this study demonstrate that altering carcass fatness will simultaneously change muscle density (indicative of changes in intramuscular fatness), and aspects of intramuscular fat content, muscle colour and juiciness. The heritabilities for the meat quality traits indicate ample opportunities for altering most meat quality traits. Moreover, it appears that colour, intramuscular fat content, juiciness, overall liking and flavour may be adequately predicted, both genetically and phenotypically, from measures of muscle density. Thus, genetic improvement of carcass composition and meat quality is feasible using in vivo measurements.
Comparison of models using different censoring scenarios for days open in Spanish Holstein cows
Authors: González-Recio O. , Chang Y.M. , Gianola D. , Weigel K. A.
Published: March 2006

Days open data from 113 569 lactation records in 774 Spanish Holstein herds were analysed using standard linear models under two different editing procedures, and with two alternative methodologies that account for censoring: a censored linear model (CLM) and a Weibull survival analysis (SA) model. The first editing procedure excluded from the linear model all censored records for days open (LMnc), and the second defined days open as days from calving to the last known insemination or culling date, treating censored records as complete (LM). Sire variance estimates for days open were 61, 70 and 139 for LMnc, LM and CLM, respectively, and 0·026 for SA on a logarithmic scale. Heritability estimates were 0·05, 0·06 and 0·08 with LMnc, LM and CLM, respectively. Rankings of sires varied between methodologies: sire evaluations from LMnc and LM had rank correlations with evaluations from SA equal to −0·65 and −0·82, respectively, and of 0·71 and 0·87 with evaluations from CLM. The rank correlation between evaluations from SA and CLM was −0·98, suggesting stronger agreement of sire rankings between models that take censoring into account.The SA model had a better predictive ability of daughter fertility at early stages of lactation than the other methods, as measured by chi-squared statistics for predicted pregnancy status at 75, 103, 140, or 200 days post partum in a split data set. The CLM also predicted daughter fertility more accurately than any of the two standard linear models.
Effects of grazing system on production and parasitism of dairy breed heifers and steers grazing wet marginal grasslands
Authors: Kristensen T. , Thamsborg S. M. , Andersen H. R. , Søegaard K. , Nielsen A. L.
Published: March 2006

Production and endoparasitism of first grazing season Holstein heifers and steers were investigated over two grazing seasons. Studies were conducted on low-lying peaty soil. In year 2000, 40 animals were included in a 2×2 factorial, replicated experiment with two sexes (steers v. heifers) and two stocking rates (SR): normal v. low (840 v. 420 kg live weight per ha at turn-out) in a set stocking grazing system. Mean grass heights over the entire season were 6·3±4·8 cm (mean±s.d.) at normal SR and 9·8±6·1 cm at low SR. Mean daily live-weight gain during grazing was significantly (P<0·001) lower at normal SR (256±147 g) compared with low (468±142 g) but sex did not significantly affect the daily gain. Serum pepsinogen levels, indicating uptake of gastric nematodes, were higher at normal SR and consistently higher in steers compared with heifers, although not significantly. In 2001 the experiment included 80 animals in a 2×2 factorial experiment with two sexes (steers v. heifers), two grazing systems (set stocking and two-paddock rotation) and four replicates. Pasture quality was low, 570 g digestible organic matter per kg organic matter and 139 g crude protein per kg dry matter on average, independent of grazing system. Mean daily live-weight gain was not significantly affected by grazing system. A tendency (P=0·07) to lower daily gain for the heifers than for steers was observed (427±161 g v. 474±138 g). Lower levels of pasture contamination with parasites were observed in the paddocks without grazing up to mid July but otherwise rotation did not prevent parasite infections. It is concluded that first grazing season steers and heifers have the same potential for growth when grazing marginal areas with low pasture quality. Set stocking or the two-paddock rotation scheme did not affect productivity or level of parasite infection at the end of season. Parasite infections became a problem at high SR. SR is an important factor for both daily live-weight gain per animal and total production per ha. However, due to the very heterogeneous structure of marginal areas there is a need for other indicators than kg live weight per ha at turn-out in order to define a clear relationship between stocking rate and production.
Nutritive value of tropical tree leaf meals in adult sows
Authors: Leterme P. , Botero M. , Londoño A. M. , Bindelle J. , Buldgen A.
Published: March 2006

Tree leaf meals (TLM) are increasingly used in the tropics to feed pigs. The nutritive value of the TLM of cocoyam (Xanthosoma saggitifolium), mulberry (Morus alba) and Trichanthera gigantea, their effect on the digestive tract and their fermentation rate in the large intestine, were determined in adult sows given diets containing 150 or 300 g TLM per kg. The TLM contained from 8·5 to 12·0 MJ digestible energy per kg dry matter (DM) and from 60 to 125 g digestible protein per kg DM. The digestibility was not affected ( P>0·05) by their rate of incorporation in the diet. The apparent ileal protein digestibility of the diets containing 300 g TLM per kg was also determined by the slaughtering method. It reached 80% for the basal diet and 54, 70 and 74% for the Trichanthera-, mulberry- and cocoyam-based diets, respectively. No diet effect ( P>0·05) was observed on the weight and length of the gastro-intestinal tract, with the exception of a heavier caecum in sows given the Trichanthera-based diet ( P<0·01). The pH of the gastric fluid of these sows was also higher ( P<0·001). The fermentation of the dietary fibre in the large intestine was evaluated by the gas technique using syringes. The cocoyam leaves presented the highest amount of total gas produced after fibre fermentation ( P<0·001). The ranking order of gas production was identical to that observed for the digestibility coefficients: Trichanthera <mulberry <cocoyam. In conclusion, TLM can represent up to 0·3 of a diet for sows. Their use in sow nutrition may be considered in tropical regions where protein sources are scarce.
Genetic relationships among objectively and subjectively assessed traits measured on crossbred (Mule) lambs
Authors: van Heelsum A. M. , Lewis R. M. , Davies M. H. , Haresign W.
Published: March 2006

Sheep farming in the UK is characterized by a crossbreeding system where ‘Longwool’ sire breeds are mated with hill dam breeds, with the crossbred (F1) ewe lambs retained for mating to terminal sires. The F1 wether and terminal-sire cross lambs are marketed for meat. At selection, F1 females are typically assessed visually for type traits relevant to dam lines, and these traits could be considered as goal traits. Their offspring and their male sibs derive their value from carcass traits. This study investigated the genetic relationships between type (subjective) and carcass (objective) traits in F1 lambs, and their potential impact on genetic improvement within this production system. Bluefaced Leicester rams were crossed with Scottish Blackface and Hardy Speckled Face ewes to produce F1 (‘Mule’) lambs. The wether lambs (no.=2197) were selected for slaughter at a target condition (a carcass fat score of 2/3L) and a number of live and carcass traits were measured. Carcass dissection data were collected on approximately one-third of these wether lambs. The ewe lambs (no.=2423) were measured for similar live traits but at a fixed age (195±5·5 days). In addition, they were subjectively assessed for a number of functional and type traits. Genetic parameters among these traits were then estimated. Heritabilities for the ewe traits were generally moderate (0·18 to 0·31) and genetic correlations between the traits were variable, with some moderate to high correlations (favourable in direction) of growth/carcass traits with overall type traits. Live weight at slaughter in wethers was highly correlated to live weight at constant age in ewes (r=0·72). In the wethers, live, cold carcass and lean weight had moderately high heritabilities (between 0·26 and 0·46), and were positively correlated with slaughter age (≥0·79). However, age at slaughter in wethers was highly negatively correlated with growth/carcass and overall type traits in ewes (between −0·45 and −0·97), perhaps reflecting differences in maturity in lambs measured at a target fatness versus age. The correlations of most other type traits in ewes with wether traits were non-significant. These results show that the subjectively assessed type traits (at least as measured in this study) will not deteriorate, and some will in fact be improved, in a selection programme aiming to improve carcass merit.
The effect of natural zeolite on nutrient digestibility, carcass traits and performance of Holstein steers given a diet containing urea
Authors: Sadeghi A. A. , Shawrang P.
Published: March 2006

The objective of this study was to evaluate effects of natural zeolite (clinoptilolite) on nutrient digestibility, carcass attributes and performance of Holstein steers given a diet containing urea. Forty-five Holstein steers (309 (s.d. 11·2) kg) were given diets as follows: control diet based on maize and soya-bean meal (SBM); treatment 2 (T2), control diet (without SBM) containing 20 g/kg urea; treatment 3 (T3), control diet (without SBM) containing 20 g/kg urea and 30 g/kg zeolite. Just before feeding, ruminal ammonia levels were low in all treatments. At 2·5 h post feeding, steers given T2 and T3 diets had higher (P<0·05) ruminal ammonia concentration than the control. At 5·5 h post feeding, steers on T3 diet had the highest ruminal ammonia concentration, which was higher (P<0·05) than the value for steers given T2 diet. Plasma urea nitrogen level increased post feeding for all treatments. At 3 h post feeding, the level for steers given T2 diet was higher (P<0·05) than those on control and T3 diets but at 6 h post feeding, the level was higher for steers on T3 diet. No differences (P>0·05) were observed in dry-matter intake among treatments. Live-weight gain and gain: food ratio were highest (P<0·05) for steers on the control diet, with no differences (P>0·05) between steers given T2 and T3 diets. Including zeolite in a diet containing urea had no effect (P>0·05) on total tract digestibility coefficients of dry matter, organic matter and crude protein but increased (P<0·05) digestibility of neutral-detergent fibre and acid-detergent fibre. Hot carcass weight and kidney, pelvic and heart fat weight of steers were highest in control, intermediate in T3 and least in T2 (P<0·05). No differences (P>0·05) were found in longissimus muscle area and fat thickness over longissimus muscle among treatments. Including 30 g/kg of zeolite in a diet containing 20 g/kg of urea decreased ruminal ammonia nitrogen concentration, plasma urea nitrogen level and increased fibre digestibility but its effect on feedlot performance was negligible.