Production of Gas Phase Zinc Oxide Nanoclusters by Pulsed Laser Ablation

We present experimental results on the photoluminescence (PL) of gas-suspended zinc oxide nanoclusters prepared during ablation of sintered ZnO targets by a pulsed ArF laser in the presence of oxygen ambient gas. The PL spectra in the UV spectral region correspond to the exciton recombination in the nanoclusters which are crystallized and cooled down to the temperature of the ambient gas in the ablation chamber. The time evolution of the spectra as well as their dependence on the ambient gas pressure are discussed.Comment: EMRS-2004, Strasbourg, France. Paper N-I.

Finite size effects, super-and sub-poissonian noise in a nanotube connected to leads

The injection of electrons in the bulk of carbon nanotube which is connected to ideal Fermi liquid leads is considered. While the presence of the leads gives a cancellation of the noise cross-correlations, the auto-correlation noise has a Fano factor which deviates strongly from the Schottky behavior at voltages where finite size effects are expected. Indeed, as the voltage is increased from zero, the noise is first super-poissonian, then sub-poissonian, and eventually it reaches the Schottky limit. These finite size effects are also tested using a diagnosis of photo-assisted transport, where a small AC modulation is superposed to the DC bias voltage between the injection tip and the nanotube. When finite size effects are at play, we obtain a stepwise behavior for the noise derivative, as expected for normal metal systems, whereas in the absence of finite size effects, due to the presence of Coulomb interactions, a smoothed staircase is observed. The present work shows that it is possible to explore finite size effects in nanotube transport via a zero frequency noise measurement

Silicon clusters produced by femtosecond laser ablation: Non-thermal emission and gas-phase condensation

Neutral silicon clusters Si_n (up to n = 7) and their cations Si_n+ (up to n = 10) have been produced by femtosecond laser ablation of bulk silicon in vacuum and investigated using time-of-flight mass spectrometry. Two populations of the Si_n+ clusters with different velocity and abundance distributions in the ablation plume have been clearly distinguished. Possible mechanisms of cluster formation (Coulomb explosion, gas-phase condensation, phase explosion) are discussed

The ocean change : management patterns and the environment

Since the 1960s, the rapid development of the international Law of the Sea has outstripped the capacity of most maritime states for developing and implementing policy. The delimitation of the Exclusive Economic Zone (EEZ), which resulted from the United Nations’ Convention on the Law of the Sea (1982) brought about an extension of its area, within which the sate exercise control over all resources and economic activities. At the same time as the jurisdiction of the state has encroached seawards, there has been a significant increase in the range of opportunities for the use of the offshore zone. Until now, the most common approach to managing Malta's marine and coastal resources has been to regulate activities. Thus, regulations concerning constructions on the foreshore, transport of sand, recreational activities on the coast, commercial fishing, control of pollution, shipping and other related marine activities exist. These regulations are not sufficient to safeguard marine resources or to ensure maximal sustainable use. Some regulations are outdated, others are not enforced and different sets of regulations may actually conflict. This situation is not unique to the coastal zone, but it is also true for the whole island. In general, Malta's development has been haphazard and piecemeal and not regulated by any national plan, formulated on the basis of a scientific study of the country's physical, economic, social and cultural characteristics, existing and projected needs and the necessity for maintaining environmental quality. Recognizing this, the Maltese government is in the process of drafting national planning guidelines in the form of the Malta Structure Plan. As a first step towards fulfilling this objective, the Planning Services Division of the Ministry for Development of Infra- structure commissioned a Coastal Zone Survey of the Maltese Islands. As part of this, a survey of the terrestrial part of the coastal zone was carried out over a six-week period from early July 1989 by a joint team from the Universities of Durham and Malta. The output of this survey comprised a report of the survey, coastal land-use maps on a scale of 1:2,500, a series of synoptic land-use maps on a scale of 1:25,000, and a series of synoptic maps on various scales, depicting coastal features of ecologjcal importance. This in the hope of determining which areas are to be preserved and which are to be used for economic gain.peer-reviewe

Supplemental Technical Data Summary M-Area Groundwater Investigation

This supplement to the Preliminary Technical Data Summary (TDS) (Gordon, 1982) presents the state of knowledge on the hydrogeology and contaminant plume characteristics in the vicinity of M Area as of October 1984. As discussed in the previous TDS, the contaminants consist of organic solvents used for metal degreasing, namely trichloroethylene, tetrachloroethylene, and 1,1,1-trichloroethane. Since the issuance of the previous TDS, the groundwater consulting firm of Geraghty & Miller, Inc. has been retained to assist with program strategy, planning, and investigative technique

Phosphorus cluster production by laser ablation

Neutral and charged phosphorus clusters of a wide size range have been produced by pulsed laser ablation (PLA) in vacuum at 532, 337, and 193 nm ablating wavelengths and investigated by time-of-flight mass spectrometry. The neutral P_n clusters are even-numbered with local abundance maxima at n = 10 and 14, while the cationic and anionic clusters are preferentially odd-numbered with (P_7)+, (P_21)+, and (P_17)- being the most abundant ions. The dominance of the magic clusters is more pronounced at 337-nm ablation that is explained by efficient direct ejection of their building blocks under these conditions. Nanocrystalline phosphorus films have been produced by PLA in ambient helium gas

Fetal MRI in the Identification of a Fetal Ventral Wall Defect Spectrum

Objective  To ascertain if useful criteria for prenatal diagnosis of fetal ventral body wall defects (VBWDs) exists by reviewing published literature on diagnosis of VBWD as compared with our own diagnostic experience. Study Design  A comprehensive literature review of diagnostic criteria of fetal VBWD including pentalogy of Cantrell (POC), omphalocele, exstrophy, imperforate anus, spina bifida (OEIS), cloacal exstrophy, limb-body wall complex (LBWC), and body stalk anomaly was performed followed by a retrospective review of all fetal magnetic resonance imaging (MRI) examinations from our medical center over a 2-year period. Results  Classically, OEIS is omphalocele, bladder exstrophy, imperforate anus, and spina bifida. POC is defects of the supraumbilical abdomen, sternum, diaphragm, pericardium, and heart. LBWC is two of the following: exencephaly or enencephaly with facial clefts, thoracoschisis or abdominoschisis, and limb defects. Twenty-four cases of VBWD on MRI over a 24-month period were identified with seven cases involving defects of additional organ systems. Six of these seven cases demonstrated findings from two or more of the traditional diagnoses POC, OEIS, and LBWC making diagnosis and counseling difficult. Conclusion  There is a lack of consensus on useful diagnostic criteria within the published literature which is reflected in our own diagnostic experience and poses a challenge for accurate prenatal counseling

Para-cresol production by Clostridium difficile affects microbial diversity and membrane integrity of Gram-negative bacteria

Clostridium difficile is a Gram-positive spore-forming anaerobe and a major cause of antibiotic-associated diarrhoea. Disruption of the commensal microbiota, such as through treatment with broad-spectrum antibiotics, is a critical precursor for colonisation by C. difficile and subsequent disease. Furthermore, failure of the gut microbiota to recover colonisation resistance can result in recurrence of infection. An unusual characteristic of C. difficile among gut bacteria is its ability to produce the bacteriostatic compound para-cresol (p-cresol) through fermentation of tyrosine. Here, we demonstrate that the ability of C. difficile to produce p-cresol in vitro provides a competitive advantage over gut bacteria including Escherichia coli, Klebsiella oxytoca and Bacteroides thetaiotaomicron. Metabolic profiling of competitive co-cultures revealed that acetate, alanine, butyrate, isobutyrate, p-cresol and p-hydroxyphenylacetate were the main metabolites responsible for differentiating the parent strain C. difficile (630Δerm) from a defined mutant deficient in p-cresol production. Moreover, we show that the p-cresol mutant displays a fitness defect in a mouse relapse model of C. difficile infection (CDI). Analysis of the microbiome from this mouse model of CDI demonstrates that colonisation by the p-cresol mutant results in a distinctly altered intestinal microbiota, and metabolic profile, with a greater representation of Gammaproteobacteria, including the Pseudomonales and Enterobacteriales. We demonstrate that Gammaproteobacteria are susceptible to exogenous p-cresol in vitro and that there is a clear divide between bacterial Phyla and their susceptibility to p-cresol. In general, Gram-negative species were relatively sensitive to p-cresol, whereas Gram-positive species were more tolerant. This study demonstrates that production of p-cresol by C. difficile has an effect on the viability of intestinal bacteria as well as the major metabolites produced in vitro. These observations are upheld in a mouse model of CDI, in which p-cresol production affects the biodiversity of gut microbiota and faecal metabolite profiles, suggesting that p-cresol production contributes to C. difficile survival and pathogenesis.Peer reviewedFinal Published versio

Effects of dredge deposits on seagrasses : an integrative model for Laguna Madre : concluding report. Volume I, Executive Summary.

Interagency Coordination Team, U.S. Army Corps of Engineers, Galveston District, The University of Texas Marine Science Institute, Texas A&M University Department of Oceanography, Texas Parks and Wildlife DepartmentThis report presents the results of an interdisciplinary collaborative effort to develop an integrative model for seagrass productivity in Laguna Madre. One of the major components of this integrative model is the Laguna Madre Seagrass Model (LMSM) which was designed to interface with other component models described in this report, including carbon and nitrogen allocation, sediment diagenesis, and spectral irradiance and radiative transfer. Linkage with hydrodynamic and sediment transport models provided a potentially valuable management tool to assess the effects of maintenance dredging and resuspension of dredged material deposits on seagrasses of Laguna Madre.Texas A&M University and the U.S. Army Corps of Engineers (Galveston District) 96-PL-03Marine Scienc