Terahertz Generation by Optical Rectification in Sugar Crystal

Journal of Infrared, Millimeter, and Terahertz Waves - We report on THz pulse generation through optical rectification of femtosecond laser pulses in sugar crystals. The sugar crystals were grown...     

In situ measurements of dissolved gases (CO2 and CH4) in a wide range of concentrations in a tropical reservoir using an equilibrator

An equilibrator system connected to an infrared photo acoustic gas analyzer was used in order to measure directly in situ the concentrations of dissolved CO2 and CH4 in waters of a tropical reservoir (Petit Saut, French Guiana). The performance of the system was tested both on a vertical profile in the stratified water body of the reservoir and in the surface waters of the river downstream the dam. Results agreed with conventional GC analysis at +/-15% in a wide range of concentrations (CO2:50-400 micromol l-1 and CH4:0.5-350 micromol l-1 corresponding to gas partial pressures of respectively 1700-13,000 and 12-8800 microatm). The time needed for in situ measurements was equivalent to water sampling, time for GC analysis in the laboratory being suppressed. The continuous monitoring of gas concentrations for 24 h in the reservoir surface waters revealed rapid changes in concentrations highly significant in the daily emission budget. The system opens new perspectives for the monitoring of gas concentrations in highly dynamic systems like tropical reservoirs.     

Monoterpene effect on feeding choice by deer

A previous study showed that Sitka black-tailed deer (Odocoileus hemionus sitkensis) consumption was negatively correlated with monoterpene content in western redcedar (Thuja plicata). To test whether these monoterpenes were deterrent to Sitka black-tailed deer, we performed feeding choice experiments with four hydrocarbon (sabinene, myrcene, -pinene, and d + l-limonene) and one oxygenated (,-thujone) monoterpene solution at their highest natural concentration in western redcedar foliage. To test whether deer response was species specific, we ran similar experiments on European roe deer (Capreolus capreolus) and rusa deer (Cervus timorensis russa). In all experiments, monoterpenes were repellent. Solutions with ,-thujone, the major monoterpene in redcedar leaves, were the most repellent of the solutions tested. We then analyzed how black-tailed and roe deer responded to (1) an increase in concentration of the monoterpenes with the weakest repellent effects (hydrocarbon monoterpenes) and (2) a decrease in concentration of the monoterpene with strongest effect (,-thujone). Repellency tended to increase with concentration for hydrocarbon monoterpenes, but remained strong for ,-thujone. As wild deer regularly feed on plants containing monoterpenes, this raises the question as to how the animals deal with these molecules.     

A multi‐tracers analysis of sources and transfers of particulate organic matter in a tropical reservoir (Petit Saut,French Guiana)

We measured the organic carbon (OC) content, the isotopic composition, the C/N ratios and the photosynthetic pigment composition of suspended matter, sediments, sediments traps and epiphytic and epilithic biofilms at the tropical Sinnamary River system (French Guiana). Our sampling included the mid‐stream reservoir lake (Petit Saut) and the estuary on the Atlantic coast. These tracers were complementary and allowed identifying different sources of particulate organic matter (POM) in the system. We found a δ¹³C–C/N signature of POM close to that of soils and litters collected in the surrounding forest, both for water column and sediment at the upstream station as well as for the sediment in a littoral zone of the reservoir, which thus indicated a terrestrial origin. Plankton communities at the centre of the reservoir were dominated by Chlorophyceae (chlorophyll a (Chl a), chlorophyll b (Chl b) and lutein) in the oxic epilimnion and by anoxygenic phototrophic bacteria, namely Chlorobiaceae (bacteriochlorophyll d (BChl d) and bacteriochlorophyll c (BChl c)) at and below the oxycline (6 m depth). In addition, this planktonic material was slightly ¹³C‐depleted due to a contribution of methanotrophic bacteria. Phytoplankton and bacterioplankton were the major source of settling material collected in the traps at all depths in the centre of the reservoir. In the traps, POM was subject to intense degradation, as revealed by C/N and isotopic data and by the presence of pheopigments. In the river downstream of the dam, Chl b, lutein, BChl c and d originating from the reservoir progressively decreased downstream as the result of mineralization. At the estuarine mouth, fucoxanthin showed the presence of diatoms and the δ¹³C‐C/N signature matched that of POM carried by the Amazonian coastal mobile mud belt. By analysing sedimentation rates in the reservoir and its outflow into the river, we were able to provide a first estimates of POM transfers in this system during the sampling period. Copyright © 2008 John Wiley & Sons, Ltd.     

Template-assisted large-scale ordered arrays of ZnO pillars for optical and piezoelectric applications

Spatially separated ZnO pillars, typically 300 nm in diameter and 2 microm in height, are fabricated via a template-directed approach that leads to long-range hexagonal order. The templates of Au nanodisk arrays are obtained by using metal membranes as a lithography mask. The growth of ZnO pillars is performed in a double-tube system through vapor diffusion-deposition. The growth mechanism of the pillars is studied in detail and is proposed to be a combination of vapor-liquid-solid and vapor-solid models. The piezoelectric and optical properties of single pillars are characterized using piezoresponse force microscopy and micro-photoluminescence spectroscopy, respectively. The pillars show strong excitonic emissions up to room temperature, which indicate a relatively low defect density and good crystalline quality. The obtained piezoelectric coefficient d(33) is (7.5+/-0.6) pm V(-1), which is to our knowledge the first reported value for a single nanopillar.     

Integrating discrete controller synthesis into a reactive programming language compiler

We define a mixed imperative/declarative programming language: declarative contracts are enforced upon imperatively described behaviors. This paper describes the semantics of the language, making use of the notion of Discrete Controller Synthesis (DCS). We target the application domain of adaptive and reconfigurable systems: our language can serve programming closed-loop adaptation controllers, enabling flexible execution of functionalities w.r.t. changing resource and environment conditions. DCS is integrated into a1 programming language compiler, which facilitates its use by users and programmers, performing executable code generation. The tool is concretely built upon the basis of a reactive programming language compiler, where the nodes describe behaviors that can be modeled in terms of transition systems. Our compiler integrates this with a DCS tool, making it a new environment for formal methods. We define the trace semantics of our contracts language, describe its compilation and establish its correctness, and discuss implementation and examples.     

The Stackelberg Minimum Spanning Tree Game

We consider a one-round two-player network pricing game, the Stackelberg Minimum Spanning Tree game or StackMST. The game is played on a graph (representing a network), whose edges are colored either red or blue, and where the red edges have a given fixed cost (representing the competitor??s prices). The first player chooses an assignment of prices to the blue edges, and the second player then buys the cheapest possible minimum spanning tree, using any combination of red and blue edges. The goal of the first player is to maximize the total price of purchased blue edges. This game is the minimum spanning tree analog of the well-studied Stackelberg shortest-path game. We analyze the complexity and approximability of the first player??s best strategy in StackMST. In particular, we prove that the problem is APX-hard even if there are only two different red costs, and give an approximation algorithm whose approximation ratio is at most min?{k,1+ln?b,1+ln?W}, where k is the number of distinct red costs, b is the number of blue edges, and W is the maximum ratio between red costs. We also give a natural integer linear programming formulation of the problem, and show that the integrality gap of the fractional relaxation asymptotically matches the approximation guarantee of our algorithm.     

Antimicrobial activity and safety of use of Enterococcus faecium PC4.1 isolated from Mongol yogurt

Screening of lactic acid bacteria strains isolated from Mongolian yogurt (Tarag) led to the isolation of Enterococcus faecium PC4.1 with a bacteriocin-like activity against Listeria genus and fungi. The antimicrobial substances in cell free supernatant were sensitive to proteolytic enzymes, while neither acidic conditions nor high temperature affected their activities. These antimicrobial substances were active after storage at 4 °C, ?20 °C and ?80 °C for over one month. The mode of action was determined as bactericidal. In the aim of further use of E. faecium PC4.1 as a biopreservative, the isolate was tested for resistance against antibiotics and for harboring virulence determinants. E. faecium PC4.1 was characterized as free from virulence factors, has low resistance to gentamicin and ampicillin but is susceptible to vancomycin.