bluuebunny/crossref_metadata_2025_split huggingface dataset:
Altered Substrate Selection of the Melibiose Transporter (MelY) of
Enterobacter cloacae
Involving Point Mutations in Leu-88, Leu-91, and Ala-182 That Confer Enhanced Maltose Transport
Authors: Shinnick Steven G. , Perez Stephanie A. , Varela Manuel F. 
Published: May 2003

ABSTRACT

We isolated mutants of
Escherichia coli
HS4006 containing the melibiose-H
+
symporter (MelY) from
Enterobacter cloacae
that had enhanced fermentation on 1% maltose MacConkey plates. DNA sequencing revealed three site classes of mutations: L-88-P, L-91-P, and A-182-P. The mutants L-88-P and L-91-P had 3.6- and 5.1-fold greater maltose uptake than the wild type and enhanced apparent affinities for maltose. Energy-coupled transport was defective for melibiose accumulation, but detectable maltose accumulation for the mutants indicated that active transport is dependent upon the substrate transported through the carrier. We conclude that the residues Leu-88, Leu-91 (transmembrane segment 3 [TMS-3]), and Ala-182 (TMS-6) of MelY mediate sugar selection. These data represent the first MelY mutations that confer changes in sugar selection.
Xenorhabdus nematophila
Requires an Intact
iscRSUA-hscBA-fdx
Operon To Colonize
Steinernema carpocapsae
Nematodes
Authors: Martens Eric C. , Gawronski-Salerno Joseph , Vokal Danielle L. , Pellitteri Molly C. , Menard Megan L. , Goodrich-Blair Heidi 
Published: May 2003

ABSTRACT

An insertion between
iscA
and
hscB
of the
Xenorhabdus nematophila iscRSUA-hscBA-fdx
locus, predicted to encode Fe-S assembly machinery, prevented colonization of
Steinernema carpocapsae
nematodes. The insertion disrupted cotranscription of
iscA
and
hscB
, but did not reduce
hscB
A expression, suggesting that
X. nematophila
requires coordinated expression of the
isc-hsc-fdx
locus for colonization.
Thermal behaviour of nitric acid dihydrate in 1:2 HNO3/H2O solutions
Authors: Lebrun N , Mahe F , Foulon M , Gors C , Petit J C 
Published: May 2003

The liquid-solid phase transitions of 1:2 HNO3/H2O solutions were investigated in bulk samples. Two forms of nitric acid dihydrate (NAD) (denoted further NAD(I) and NAD(II)) can precipitate. After cooling down to 200 K, NAD(I) crystallizes and melts congruently at 238 K. On cooling down to 173 K, NAD(I) first crystallizes and a polymorphic form NAD(II) appears on heating at about 210 K, which is governed by a nucleation process at temperatures below 200 K. NAD(II) then transforms into nitric acid trihydrate at 235 K via a peritectic reaction. The existence of the two forms is confirmed by Raman studies. Our infrared experiments on bulk samples are in good agreement with those reported in the literature leading to the conclusion that the NAD(I) studied here is also observed in polar-stratospheric-cloud (PSC) particles. In stratospheric conditions, NAD(II) probably cannot freeze in the PSC particles. PACS Nos.: 64.70, 64.60, 61.10, 05.70
Segregation, transport, and interaction of climate proxies in polycrystalline ice
Authors: Rempel A W , Wettlaufer J S 
Published: May 2003

The most detailed records of the Earth's climate during the past few hundred millennia are derived from ice cores retrieved from Greenland and Antarctica. The analyses of these records assume that the distributions of the trace constituents that are used as proxies for past climate have not significantly altered since deposition at the surface, and yet careful studies, at high spatial resolution, have identified core segments where appreciable post-depositional changes have occurred. To improve the reliability and resolution of paleoclimate interpretations, we have examined the mechanisms underlying the transport and interaction of climate proxies in polycrystalline ice, many of which are soluble impurities that are found principally in premelted liquid that lines the boundaries between ice grains. We find that the rate of post-depositional alteration depends critically on where the trace constituents reside; whether in the premelted liquid, in which case they exert a controlling influence on the total volume fraction of liquid that is present, or in the grains themselves. In the former case, the premelted liquid reservoir contains the principle conduits through which many of the impurities are transported and interact, and in the latter case, the temporal evolution of impurity concentration is both slower and more complex. We provide quantitative models that describe these processes and highlight the importance of impurity segregation for our understanding of past climates. PACS Nos.: 66.30Jt, 91.60Ed, 92.40Sn, 92.40Vq, 92.70-j
Compressive strength of iceberg ice
Authors: Jones S J , Gagnon R E , Derradji A , Bugden A 
Published: May 2003

The uniaxial compressive strength of iceberg ice was determined over a wide range of strain rates from 108 to 10+1 s1 at 10°C. It was found that for strain rates less than 104 s1, strength increased in a power-law manner with strain rate. Above 104 s1, the strength was essentially constant at 4 MPa, dropping slightly between 103 and 101 s1, before rising again to a value of about 10 MPa at 10+1 s1. Thin sections of the ice revealed a small grain size of about 3.5 mm and elongated air bubbles with a ratio of length to width of about 10. In the practical strain-rate range of interest, the maximum failure stress observed was 4.8 MPa. PACS No.: 62.20
Point defects and electrical properties of ice
Authors: Whitworth R W 
Published: May 2003

This paper is a brief summary of a review lecture in which the essential features of the standard theory of electrical properties of ice were described and attention was drawn to current problems concerning the nature of protonic point defects on which the theory is based. PACS Nos.: 61.72Ji, 66.10Ed, 66.30Dn, 77.22
Strain and temperature dependence of crack populations in columnar-grain ice
Authors: Gold L W 
Published: May 2003

It has been shown that the development of grain-boundary and transgranular crack populations in transverse isotropic columnar-grain ice by a uniaxial compressive stress is a random process. The lognormal distribution function was found to be a good descriptor of the strain dependence of the crack density and of the crack length. It is shown, in the present paper, that the populations are induced in the first 102 strain and within the time range for the anelastic strain. These time and strain limits, and the strain-rate, stress, temperature, and grain-size dependence of the characteristics of the crack populations, indicate a two-stage process involving the development of precursors and the formation of cracks. The increasing probability for the formation of grain-boundary cracks with increasing strain rate is consistent with a time-dependent growth of voids and an increase in the associated stress intensity factors. The increasing probability for the formation of transgranular cracks with decreasing stain rate is consistent with an increasing density of dislocations and grain distortion due to shear. PACS Nos.: 62.20MK, 62.40-x
The magnetic properties of oxygen-hole aluminum centres in crystalline SiO2. VI: A stable AlO4/Li centre
Authors: Walsby C J , Lees N S , Claridge R FC , Weil J A 
Published: May 2003

A new study, by electron paramagnetic resonance (EPR) spectroscopy at cryogenic temperatures, of aluminum oxygenic-hole centres in a α-quartz single crystal is reported. The well-known centre [AlO4]0 has been reinvestigated with somewhat improved techniques and computer analysis, confirming previous results in the literature. A previously unreported AlLi centre has now been well characterized by EPR. From the fitted parameter matrices g, A(27Al), P(27Al), A(7Li), and P(7Li) we have determined not only that the hole resides on a "long-bonded" oxygen anion, as in [AlO4]0, but have also established the position of the near-by interstitial lithium ion. One model for this centre is that it consists of a lithium atom Li0 linked to the diamagnetic centre [AlO4], yielding hole-bearing species [AlO4/Li] via internal charge transfer. PACS Nos.: 7630Da, 7630Mi
Ice nucleation by kerosene soot under upper tropospheric conditions
Authors: Suzanne J , Ferry D , Popovitcheva O , Shonija N K 
Published: May 2003

Quasi-elastic neutron scattering (QENS) and neutron diffraction (ND) experiments were conducted to characterize the dynamics and structure of water/ice confined in a well-defined kerosene-soot pores network at 40, 60, and 100% relative humidity and at temperatures from 283 to 204 K. The QENS spectra indicate that about 35% of the adsorbed water is in an amorphous solid-like state at T = 283 K and that an appreciable amount of liquid water exists in the soot supermicropores down to the lowest temperature investigated, i.e., 204 K. The depression in freezing temperature is related to the pore dimensions. At T [Formula: see text] 260 K ND shows a mixture of amorphous ice, probably located in the soot mesopores coexisting with ice Ih at the surface of the soot primary particles. The results are discussed within the context of aircraft-generated soot aerosols in the upper troposphere as candidates for heterogeneous ice nucleation responsible for contrails and cirrus formation. PACS Nos.: 82.33Tb, 92.60Mt, 81.05Rm, 61.12-q
Measured temperature and pressure dependence of compressional (Vp) and shear (Vs) wave speeds in compacted, polycrystalline ice Ih
Authors: Helgerud M B , Waite W F , Kirby S H , Nur A 
Published: May 2003

We report on laboratory measurements of compressional- and shear-wave speeds in a compacted, polycrystalline ice-Ih sample. The sample was made from triply distilled water that had been frozen into single crystal ice, ground into small grains, and sieved to extract the 180250 µm diameter fraction. Porosity was eliminated from the sample by compacting the granular ice between a hydraulically driven piston and a fixed end plug, both containing shear-wave transducers. Based on simultaneous compressional- and shear-wave-speed measurements, we calculated Poisson's ratio and compressional-wave, bulk, and shear moduli from 20 to 5°C and 22 to 33 MPa. PACS Nos.: 91.60Lj
Iceice friction measurements, and water lubrication and adhesion-shear mechanisms
Authors: Maeno N , Arakawa M , Yasutome A , Mizukami N , Kanazawa S 
Published: May 2003

The results of systematic measurements of iceice friction coefficients are summarized and the applicability of the two physical mechanisms of ice friction, namely, the water lubrication and the adhesion-shear deformation of ice, are discussed. PACS Nos.: 68.35Np, 81.20Ev, 81.40Pq, 83.80Nb
Structural studies of gas hydrates
Authors: Klapproth A , Goreshnik E , Staykova D , Klein H , Kuhs W F 
Published: May 2003

An overview of recent structural work focusing on the gas hydrates of methane and carbon dioxide is given. Both the crystal structure and the microstructure are considered. We report on the pressure-dependent molecular structure of methane clathrate hydrate using laboratory-made hydrogenous and deuterated samples investigated by neutron and hard-X-ray synchrotron diffraction experiments. The isothermal compressibilities are determined for hydrogenated and deuterated CH4 hydrate, and isotopic differences between both compounds are established for the first time. The cage filling of carbon dioxide and methane hydrate is determined and compared with predictions from statistical thermodynamic theory. In the case of small cages in methane hydrate, experimental results and predictions do not agree. Field-emission scanning electron microscopy reveals the meso- to macro-porous nature of gas hydrates formed with an excess of free gas. Furthermore, in situ measurements of the formation kinetics of porous hydrates are reported in which differences between methane and carbon dioxide are established quantitatively and the transient existence of a type II carbon dioxide structure is found. PACS Nos.: 82.75-z, 61.10Nz, 61.12Ld, 68.37Hk
High-pressure Raman and Brillouin studies of single crystalline gas hydrates
Authors: Shimizu H 
Published: May 2003

Methane hydrate (MH) and argon hydrate (AH) single crystals were synthesized in a diamond anvil cell to investigate their intrinsic high-pressure properties by visual observation and in situ Raman and Brillouin-scattering measurements. Single crystalline MH shows clearly two phase transitions at P =0.9 and 1.9 GPa in its crystalline shape and state under a microscope, and in the change in its Raman spectra of CH stretching vibrations of guest CH4 molecules. The first determination of the elastic properties in MH sI phase has revealed that MH is about 10% softer than the most common ice Ih, which is accounted for by MH's void-rich and open structures. For a single-crystal AH, we have observed two phase transitions from AH-I (sII) to AH-II at about P =0.65 GPa and from AH-II to AH-III at P =1.02 GPa. The breakdown of the cage structure in AH-III was confirmed by the disappearance of the OH stretching mode of host H2O lattices. The possibility of Ar double occupancy in the large cages of sII and higher pressure phases is investigated by the low-frequency Raman peak observed around 120 ~ 140 cm1 in view of recent MD calculations. PACS Nos.: 62.30+d, 62.50+p, 62.65+k, 64.70-p, 78.30-j, 78.35+c
A sapphire cell for high-pressure, low-temperature neutron-scattering experiments on gas hydrates
Authors: Rondinone A J , Jones C Y , Marshall S L , Chakoumakos B C , Rawn C J , Lara-Curzio E 
Published: May 2003

A single-crystal sapphire cell for performing neutron-scattering experiments on gas hydrates synthesized in situ was designed and fabricated to operate at pressures up to 350 bar (1 bar = 105 Pa) and temperatures between 10 and 300 K. The single-crystal cell is cut off-axis from the c-axis of sapphire to avoid Bragg diffraction in the scattering plane for the DebyeScherrer geometry. The cell is pressurized from a boosted pumping station via a small-diameter stainless-steel pipe. The cell is cylindrical with no external supports. The design of the cell allows the unobstructed detection of neutrons scattered from the sample. This requirement necessitated a departure from the predominant style of sapphire cells reported in the literature. Several iterations of design modifications and finite-element modeling were performed prior to building the prototype. The cell was tested hydrostatically at room temperature. Preliminary inelastic neutron scattering data are reported to verify the performance of the cell. PACS No.: 61.12ex
The microstructural location of impurities in ice
Authors: Baker I , Cullen D , Iliescu D 
Published: May 2003

The microstructural locations of impurities in natural ice have been of interest for over a century, but only in recent years have efforts been made to determine their location. Here, we outline the few measurements that have been performed. The focus is on a technique that we developed, which has also been subsequently used by others, that involves the controlled sublimation of uncoated ice in a low-vacuum scanning electron microscope. This process leaves behind concentrated impurities, in both the grain boundaries and the grain interiors, which are then identified using energy dispersive X-ray microanalysis. An overview of observations on meteoric ice from both Greenland and Antarctica; on accretion ice from Vostok Station, Antarctica; and on temperate pond and river ice is presented. PACS No.: 61.72-y
Inelastic neutron scattering and molecular dynamics studies on low-frequency modes of clathrate hydrates
Authors: Itoh H , Chazallon B , Schober H , Kawamura K , Kuhs W F 
Published: May 2003

Low-frequency modes of gas hydrates with Xe, Ar, O2, and N2 atoms/molecules have been studied by inelastic neutron-scattering and molecular dynamics simulations. Type I and type II clathrate hydrates show some small but significant differences of the low-frequency host contribution to the density of states. Both differ markedly from that of ice Ih and depend only weakly on the guest. The vibrational modes associated with Xe atoms were observed at 2.2, 2.9, and 4.0 meV (T = 100 K). They are in good agreement with predictions from molecular dynamics simulations. In the case of N2 hydrate we found a well-defined peak at about 2 meV, which shows a remarkable shift to higher frequency with increasing temperature. This peak and a broad peak that is overlapped with the host lattice modes (6.5 and 10.5 meV) are assigned to the vibration of N2 molecules in the large and small cages, respectively. The calculated vibrational spectra of N2 molecules in doubly occupied large cages show a significant distinct spectral distribution. The anharmonic shift of the guest atoms in large cages is significantly less pronounced in Xe hydrates suggesting that guest-host interactions can vary considerably from one system to another. PACS Nos.: 82.75-z, 78.70N, 71.15Pd, 63
Coexistence of structure I and II hydrates formed from a mixture of methane and ethane gases
Authors: Takeya S , Kamata Y , Uchida T , Nagao J , Ebinuma T , Narita H , Hori A , Hondoh T 
Published: May 2003

X-ray diffraction measurements were conducted to determine the hydrate structures formed from a mixture of CH4 and C2H6 gases at 263 K. With increasing initial fractions of C2H6 in the gas, the crystal structures of the hydrate were structure I, structure I + structure II, structure II, structure I + structure II, and structure I. In situ observations of the growth processes of the mixed gas hydrates under constant gas concentration suggest that the coexistence of structure I and structure II hydrate were caused by occurrences of metastable hydrate structure. PACS No.: 82.75Fq
Photo-oxidation of SO2 and of SO2 trapped in amorphous water ice studied by IR spectroscopy. Implications for Jupiter's satellite Europa
Authors: Schriver-Mazzuoli L , Schriver A , Chaabouni H 
Published: May 2003

Fourier Transform Infrared Spectroscopy (FTIR), is used to characterize thin films of sulfur dioxide trapped in excess of amorphous water ice and to study the photo-oxidation of pure solid SO2 or of SO2 diluted in water ice. These laboratory experiments were undertaken in an attempt to find information on the formation of hydrated sulfuric acid detected on Europa's surface. Vibrational spectra at 30 K of mixed films containing SO2 with an excess of water depend on the deposition conditions. A metastable (SO2)m(H2O)n phase and a solid solution of SO2 in water ice have been evidenced. Irradiation at 266 nm of mixed films SO2/O3/H2O produces sulfur trioxide and hydrogen peroxide without traces of sulfuric acid. Irradiation of films of pure SO2, under 200 nm, leads to sulfur trioxide and to ozone. When SO2 is diluted in amorphous water ice, new weak bands that appear after irradiation suggest the formation of sulfuric acid. PACS No.: 82.50Hp
Neutron-scattering studies of the phase transitions in high-pressure ices during annealing
Authors: Wang Y. , Kolesnikov A I , Dong S L , Li J C 
Published: May 2003

Inelastic incoherent neutron scattering was used to study the phase transition process of high-density amorphous (HDA) ice to low-density amorphous (LDA) ice by thermal treatment. The results show that when the annealing temperature is lower than 136 K no obvious phase-transition is observed, and transformation of the HDA ice to the LDA ice occurs between 136 and 144 K. From comparison of the measured inelastic neutron-scattering spectra for HDA ice and ice Ih, it is found that the internal interactions (covalent bond OH and three-body interaction HOH) are stronger in HDA ice, which correlates with the longer nearest OO distances in HDA ice compared to ice Ih (2.80 and 2.75 Å, respectively). The report also discusses the differences in vibrational spectra of LDA ices obtained by different methods (annealing HDA ice and depositing water vapour on a cold substrate). PACS No.: 64.60-i
THE MOST REFINED VASSILIEV INVARIANT OF DEGREE ONE OF KNOTS AND LINKS IN ℝ1-FIBRATIONS OVER A SURFACE
Authors: Tchernov Vladimir 
Published: May 2003

As it is well-known, all Vassiliev invariants of degree one of a knot K ⊂ ℝ3 are trivial. There are nontrivial Vassiliev invariants of degree one, when the ambient space is not ℝ3. Recently, T. Fiedler introduced such invariants of a knot in an ℝ1-fibration over a surface F. They take values in the free ℤ-module generated by all the free homotopy classes of loops in F. Here, we generalize them to the most refined Vassiliev invariant of degree one. The ranges of values of all these invariants are explicitly described. We also construct a similar invariant of a two-component link in an ℝ1-fibration. It generalizes the linking number.
ANGIONEOGENESIS AROUND INDUCED BONE WITH RECOMBINANT HUMAN BMP-2 IN A LATISSIMUS DORSI MUSCLE FLAP
Authors: Akioka Jiro , Kusumoto Kenji , Bessho Kazuhisa , Sonobe Junya , Kaihara Shinji , Wang Yibiao , Iizuka Tadahiko , Ogawa Yutaka 
Published: May 2003

Bony tissue induced with recombinant human bone morphogenetic protein-2 (rhBMP-2) in the latissimus dorsi muscle flap (LDMF) of rats was investigated in angiography and histological examination. In five rats, rhBMP-2 with atelopeptide type I collagen (CL) as a carrier was implanted in the muscle pocket of LDMF. In five controls, only CL was implanted in the same manner. Three weeks after the implant, contrast medium was injected into the assending aorta. The LDMF was cut off at the base and exposed in soft X-ray. The implant and the surrounding tissue were then histologically examined. In the rhBMP-2-implant group, the vascularity was richer, especially around the implant, and radiated to the induced bony tissue. Contrast medium was observed in the vascular cavities of the marrow inside the trabeculae. In the controls, the vascularity was relatively poor and the remnant CL occupied the whole implant space. This study indicated that rhBMP-2 does not only induce trabeculae in muscle tissue, but also in the marrow, including vessels in the implant and the vascular system around the implant. Then, the induced bony tissue is supported in the circulation by the circulation by the vascular system, as a functional osseous tissue. This phenomenon may be highly beneficial in endogenous tissue engineering and regenerative medicene for skeletal reconstruction using BMP in the future.
BMP-7 IN ORTHOPEDIC APPLICATIONS: A REVIEW
Authors: Giltaij Lex R. 
Published: May 2003

In recent years, significant progress has been made on the research of Bone Morphogenetic Protein-7, BMP-7 (OP-1). BMP-7 is a growth- and differentiating-factor and a member of the TGF-β or Transforming Growth Factor-beta Superfamily. Ever since recombinantly produced human BMP-7 (rhBMP-7) became available in the early 1990s research in this area intensified. Many publications and presentations were issued detailing the ability of rhBMP-7 to induce new bone formation and to investigate this as an option to solve a wide variety of orthopedic problems.BMP-7's activity in bone regeneration has been established through numerous animal trials. Work has been presented on the potency of rhBMP-7 in joint revision arthroplasty, fracture healing and spinal fusion. rhBMP-7 has been investigated in a prospective controled human trial as an alternative for autograft in the treatment of tibial non-unions. In the not too distant future surgeons may have a new tool available in their daily practice for stimulating regeneration of bone and other skeletal tissue, though still many question on issues like dosing, predictability of outcomes, suitable indications and surgical techniques remain yet unanswered.