Spinal cord injury (SCI) leads to axonal damage and limits the ability of the brain to communicate with the rest of the body. Several bioengineered approaches have been developed for the recovery of SCI. Among these techniques, degradable guidance tubes have shown promising results. However, design of nerve guide tubes requires several design considerations and has been a significant challenge. To assess the efficacy of a prototypical implanted nerve guide tubes, it is essential to perform continuous monitoring. In this respect, magnetic resonance imaging (MRI) is one of the most reliable imaging techniques as it offers the ability to achieve extraordinary high temporal and spatial resolution in addition to its non-invasive features. In spite of the excellent image quality of non-enhanced MRI various types of contrast agents have been developed to further enhance the contrast and allow improved visualization. The MRI contrast agents principally work by shortening the T1 or T2 relaxation times of protons located nearby. The presented study was intended to evaluate the in vitro degradation of the nerve guide tubes made of poly (lactic-co-glycolic acid) (PLGA). PLGA tubes incorporated with different concentrations of superparamagnetic iron oxide (SPIO) were scanned by MRI 3T on weekly basis during the degradation period. Spin-echo (SE) sequence with various echo times (TEs) ranged from 13.3 to 314.4 msec was applied. T2 mapping was computed using in-house algorithm developed in Matlab. Least square fit was used to find the slope of the decay curve by plotting log intensity on the y-axis and echo time on the x-axis. The average T2 values were calculated. Mass loss and water uptake of the degrading tubes were also measured weekly. Moreover, the micro-structural changes of the tubes were investigated using the scanning electron microscope (SEM). The MRI results showed that the concentration of SPIO affects the signal intensity of the T2 weighted images reducing the T2 relaxation time value. Accordingly, a linear correlation between SPIO concentration and T2 relaxation time was found. At the beginning of degradation, the SPIO nanoparticles were trapped within the polymeric network. Therefore, water penetration was the predominant factor affecting the T2 relaxation times. At week 5, a significant mass loss was observed. From this stage onwards, the trapped SPIO were released from the polymeric network increasing T2 relaxation time dramatically. According to SEM images, the size of the pores in PLGA guide tubes was increased with the degradation. Approaching the end of degradation, shrinkage of the tubes was observed and the degraded nerve guide tubes were shown to be collapsed. Similar shape variation was observed in T2 weighted MR images. In summary, this study provided an approach to non-invasive monitoring of degradation behavior of nerve guide tubes using contrast enhancement. The developed technique is of great importance since it opened an insight to non-invasive monitoring of tissue engineered scaffolds for in vivo studies.

No description available.

The ambient temperature of an environment has potential to influence many aspects of the behavior and physiology of small-bodied ectotherms, including brush-legged Wolf spiders Schizocosa ocreata (Hentz, 1844) (Araneae: Lycosidae). Temperature varies significantly, and often unpredictably, in their habitat throughout the spring breeding season, and is known to influence male Schizocosa courtship behavior. Currently unknown is what effect fluctuations in ambient temperature alone might have on critical, non-behavioral sexual signals such as female silk and chemical cues. We collected cues from mature, virgin females and subjected each sample to one of three thermal treatments (40°C, 20°C, or -12°C), at constant humidity. We presented treated female cues to mature males and recorded male response across treatment types as a behavioral indicator of signal degradation. There were no significant differences across treatments in the frequency or duration of male behaviors, including critical courtship and exploratory behaviors. Our results suggest that thermally induced degradation of female sexual signals is negligible for this species and likely has little or no influence on male behavior.

Amongst the most threatened ecosystems on Earth, mangrove forests are also one of the more difficult to work in due to their growth in mud and open water coastal zones and their dense tangled stems, branches and prop roots. Consequently, there has been an impetus to employ remotely sensed imagery as a means for rapid inventory of these coastal wetlands. To date, the majority of mangrove maps derived from satellite imagery utilize a simple mangrove classification scheme which does not distinguish mangrove species and may not be useful for conservation and management purposes. Although more elaborate satellite based mangrove classification schemes are being developed, given their enhanced complexity they deserve additional justification for end users. The purpose of this study was to statistically examine the appropriateness of one such classification scheme based on an inventory of field data. In January of 2007 and May of 2008, 61 field sample plots were selected in a stratified random fashion based on a previous classification of a degraded mangrove forest of the Isla La Palma (Sinaloa, Mexico) using Landsat TM5 data. Unlike other previous Landsat TM based classifications of this region, which simply identified the mangrove forests as one class, the mangroves were classified (i. e. mapped) according to four conditions; healthy tall, healthy dwarf, poor condition, and dead mangroves. Within each sample plot, all mangroves of diameter of breast height (dbh) greater than 2.5 cm were identified and their height, condition and dbh recorded. An estimated Leaf Area Index (LAI) value also was obtained for each sample and the shortest distance from the center of each sample plot to open flowing water was determined using a geographic information system (GIS) overlay procedure. These data were then used to calculate mean values for the four classes as well as to determine stem densities, basal areas, and the Shannon-Wiener diversity index. In order to assess the appropriateness of this mangrove classification scheme a discriminant analysis approach was then applied to these field data. The results indicate this forest has undergone severe degradation, with decreasing mean tree heights, mean dbh and species diversity. In regards to the discriminant analysis procedure, further classification of these field plots and cross-validation based on these significant variables provided high classification accuracy thus validating the appropriateness of the satellite based image classification scheme. Moreover, the discriminant analysis indicated that the estimated LAI, mean height, and mean dbh are significant in the separation of the classification of mangrove forest condition along these field sample plots.

Given the scale and rate of mangrove loss globally, it is increasingly important to map and monitor mangrove forest health in a timely fashion. This study aims to identify the conditions of mangroves in a coastal lagoon south of the city of Mazatlán, Mexico, using proximal hyperspectral remote sensing techniques. The dominant mangrove species in this area includes the red (Rhizophora mangle), the black (Avicennia germinans) and the white (Laguncularia racemosa) mangrove. Moreover, large patches of poor condition black and red mangrove and healthy dwarf black mangrove are commonly found. Mangrove leaves were collected from this forest representing all of the aforementioned species and conditions. The leaves were then transported to a laboratory for spectral measurements using an ASD FieldSpec® 3 JR spectroradiometer (Analytical Spectral Devices, Inc., USA). R2 plot, principal components analysis and stepwise discriminant analyses were then used to select wavebands deemed most appropriate for further mangrove classification. Specifically, the wavebands at 520, 560, 650, 710, 760, 2100 and 2230 nm were selected, which correspond to chlorophyll absorption, red edge, starch, cellulose, nitrogen and protein regions of the spectrum. The classification and validation indicate that these wavebands are capable of identifying mangrove species and mangrove conditions common to this degraded forest with an overall accuracy and Khat coefficient higher than 90% and 0.9, respectively. Although lower in accuracy, the classifications of the stressed (poor condition and dwarf) mangroves were found to be satisfactory with accuracies higher than 80%. The results of this study indicate that it could be possible to apply laboratory hyperspectral data for classifying mangroves, not only at the species level, but also according to their health conditions.

Cigarette smoke is suspected to cause diverse illnesses in smokers and people breathing second- and third-hand smoke. Although different studies have been done to elucidate the impact on health due to smoking, there is a lack of kinetic information regarding the degradation of nicotine under different environmental conditions. As a consequence, currently it is not possible to determine thoroughly the risk due to exposure to nicotine and the compounds derived from its decomposition. With the aim of contributing to clarify the different degradation paths followed by nicotine during and after the consumption of cigarettes, this work presents a theoretical study of the hydrogen atom abstraction reaction by hydroxyl radical at four sites in the nicotine molecule in a broad range of temperature, specifically be-tween 200-3000 K. The site-specific kinetic rate constants were computed by means of the multi-structural torsional variational transition state theory with small curvature tunneling contribution, performing ab initio calculations at the level M06-2X/aug-cc-pVQZ//M06-2X/cc-pVTZ. According to our computations, the dependence on temperature of the studied rate constants exhibited a non-Arrhenius fashion, with a minimum at 873 K. A negative temperature dependence was observed at temperatures lower than 873 K, indicating more prolonged exposure to nicotine in warmer environments. On the other hand, the opposite behavior was observed at higher temperatures; this non-Arrhenius be-havior results of interest in tobacco cigarette combustion, inducing different reaction mechanisms depending on the burning conditions of the different smoking devices. The results indicate that multi-structural and torsional anharmonicity is an im-portant factor in the computation of accurate rate constants, especially at high tem-peratures where the higher-energy conformers of the different species exert a larger influence. The anharmonicity factors suggest that disregarding the anharmonic de-viations leads to overestimation of the rate constant coefficients, by a factor between four and six. Our computed overall kinetic rate constant at 298 K exhibited very good agreement with the only experimental value meausred by Borduas et al. [1], af-fording certainty about our calculated site-specific rate constants, which are currently inaccessible to experiments. However, further experimental studies are necessary to validate our kinetic studies at other temperatures.

This study examined three aspects: estimation of chimpanzee (Pan troglodytes) population size using nest density as a proxy, description of the plant community and assessment of human impacts to chimpanzee habitat in Kwitanga forest, western Tanzania. The overall estimated mean chimpanzee population density was 0.69(0.31–1.54) individuals per km2 and a mean population size of 15(7-34) weaned individual chimpanzees in the forest. The natural vegetation in Kwitanga consists mainly of miombo woodland, dominated by Brachystegia-Julbernadia tree species, poorly developed riverine forest, cultivated land and oil palm plantation. Assessment of the abundance of nesting trees in the landscape revealed that tree species composition along transects were significantly different to nesting sites (trees surrounding the actual tree that contains a nest) (Kolmogorov-Smirnov test: KSa = 2.0148; D = 0.3934: P < 0.05). Thirteen tree species were used for nests; the most used species were B. bussei, B. utilis, B. mirophylla, J. globiflora and P. tinctorius. The assessment on scarcity of nesting tree species in the landscape revealed that such species were abundant by proportion (KSa = 0.5883; D = 0.2308; P > 0.05), and species-specific density (Wilcoxon Z-test: Z = - 1.0265; U1= U2 = 13; p > 0.05). Trees in size classes between 10 cm and 40 cm diameter dominated the forest. The study on size suitability showed that there were significant differences (using ANOVA with Tukey’s HSD post hoc test) in tree diameter size among the three groups: transects, nesting sites, and nesting trees. Nesting trees were unique in size to the other two groups. The mean size of nesting trees was larger compared to both nesting sites and transects (27 ± 1.1 cm; 23 ± 0.7 cm and 18 ± 0.5 cm) respectively. Similar differences existed in tree densities between nesting sites and transects (Wilcoxon test: Z = 1.8104; U1 = 46, U2 = 61: P< 0.05), with nesting sites presenting higher tree density. These results indicated scarcity in trees of a size suitable for nesting, and nesting materials.. Nesting tree species occur in the landscape, though their sizes and higher tree species density at nesting sites determined nesting location choice and specific nesting tree selection. Tree felling indicated by stumps was the major threat to the availability of suitable nesting trees, with a higher encounter rate of seven (7) stumps per km and contributed 48 % of total human disturbance, followed by established fields in the forest. The analysis on the direction of the major threat to the habitat revealed that, the main road cutting through the forest is a key to tree felling. Encountered stumps declined with increased distance from the main road towards the forest edge, with more stumps in between 0 -100 m (P< 0.05; log (Y) = 1.7017 - 0.0007(X); R2 = 0.6705). Such findings implied that the prison inside the forest is a iii major cause of habitat decline. At least 30 tree species constituted the group of stumps. Julbernadia globiflora and Uapaca kirkiana were the most felled tree species. High human disturbances implied by higher human activities encounter rates, and overlapping tree size classes between felled and standing trees were the major threats to chimpanzee habitat in Kwitanga forest. High chimpanzee density and population size estimates in Kwitanga forest renders this area a potential for conservation in the Greater Gombe Ecosystem Program. Kwitanga being the largest remaining natural forest near Gombe National Park, it will increase habitat size to allow chimpanzee dispersal and feeding area. Such movements across heterogeneous landscapes would allow long-term survival through reduced competition, increased genetic diversity and ability to absorb minimal environmental shocks

Oleaginous microbes can accumulate over 20% of their cell dry weight as lipids that are stored as intracellular energy reserves. The characterization of other oleaginous bacteria creates opportunities for the development of alternative feedstocks and technologies. Rhodococcus rhodochrous is a gram-positive bacterium known for its biodegradation capabilities, but little is known about its ability to accumulate lipids. As R. rhodochrous is capable of degrading hydrocarbon gasses and other aromatics, this study aims to investigate any associated lipid production during the conversion of waste and nontraditional carbon sources, such as model lignocellulosic inhibitors. Lignocellulosic biomass is the most abundant and renewable organic material in the world and is composed of cellulose, hemicellulose, and lignin, which can be pretreated to release sugars from the complex, and often recalcitrant, lignin polymer for microbial fermentation. R. rhodochrous was cultivated with various carbon sources, including glucose, xylose, acetic acid, furfural, phenol, vanillic acid, hydroxybenzoic acid, and propane. The results suggest that R. rhodochrous can survive in the presence of these compounds, achieving almost 7g/L cell dry weight after 168 hours and still accumulate up to 40-50% of cell dry weight as lipid in glucose supplemented media. Furthermore, the aromatic compounds are undetected after 48 hours indicating that R. rhodochrous was able to tolerate these compounds and accumulate lipids. Fatty acid methyl ester profiles show a prevalence of palmitic and oleic methyl esters. Overall, these studies are contributing to a better understanding and characterization of another oleaginous Rhodococcus species, Rhodococcus rhodochrous.

Renewable polymers (bioplastics) offer an alternative to petroleum-based polymers and reduced environmental impact through decreased petroleum dependence and a sustainable product lifecycle via renewable, biomass-derived monomers and completely degradable polymers. Applying green chemistry principles, melt polycondensations of 1,3-propanediol with malonic acid and 1,3-propanediol with itaconic acid were performed to produce poly(trimethylene malonte) (PTM) and poly(trimethylene itaconate) (PTI), respectively. Aluminum chloride was used as the catalyst and reaction temperatures from 125-175 °C and reaction times from 2-32 h were attempted in order to produce high yields and molecular weights (Mw). Gravimetric yields ranged from 20-95 wt.% for PTM and 20-85 wt.% for PTI. Both PTM and PTI contained ester and ether backbone bonds, as determined by Fourier transform infrared and nuclear magnetic resonance spectroscopy. Gel permeation chromatography showed both PTM and PTI to have a bi-modal Mw distributions centered at 1.4±0.1 kDa and 35±3 kDa for PTM and 1.0±0.1 kDa and 38±2 kDa for PTI. For PTM, a Tg of -64 °C and a Tm of 29 °C was identified using differential scanning calorimetry (DSC). A crystallization temperature for PTI was found at ~160 °C using DSC. A hydrolytic degradation study was performed at 25 °C on PTM and PTI in pH 5.4, 7, 9, and 11 aqueous solutions for up to 4 weeks. The introduction of K+ ions (in the KOH aq. solutions) interfered with the AAC2 and AAL1 ester hydrolysis mechanisms through acid-base interactions. PTM was found to be susceptible to hydrolytic degradation and lost ~37 wt.% through ester hydrolysis and showed a molecular weight reduction of ~0.8 kDa over 10,000 min for a pH range of 7 to 11. PTI was also found to be susceptible to hydrolytic degradation with ~22 wt.% decrease through ester hydrolysis and molecular weight reduction of ~0.25 kDa over 10,000 min for a pH range of 7 to 11. PTM is a low molecular weight, saturated, linear copolymer and PTI is a low molecular weight, unsaturated, branched copolymer. Both PTM and PTI are renewable copolymers produced using green chemistry and mild reactions conditions and were found to be susceptible to hydrolytic degradation.

No description available.