Mechanical,machining and corrosion properties of Al5083-carbon nanotubes composite produced by friction stir processing

In the current work, composites of Al5083 aluminum alloy and carbon nanotubes were developed by friction stir processing. Grain size reduction was observed in the composite from a starting size of 115 μm±4.6 μm to 11 μm±3.3 μm. Higher hardness, yield strength and ultimate tensile strength were measured for the composite at the cost of losing ductility compared with friction stir processed Al5083 and base alloy. This behavior can be understood by considering the influence of grain size and carbon nanotubes. Machining studies carried out by conducting drilling experiments demonstrate decreasing cutting forces for the composite compared with friction stir processed Al5083. However, compared with base alloy, composite exhibited higher cutting forces at all of the cutting parameters. Corrosion behavior of the materials assessed by electrochemical tests demonstrates the promising effect of grain refinement on enhancing the corrosion resistance of friction stir processed Al5083. However, presence of carbon nanotubes marginally decreased the corrosion resistance of composite compared with friction stir processed Al5083. From the results, it can be understood that the addition of carbon nanotubes significantly enhance the mechanical properties and machinability. However, addition of carbon nanotubes on decreasing the corrosion performance is a noteworthy observation.     

Effects of adrenal steroids on basal ganglia neuropeptide mRNA and tyrosine hydroxylase radioimmunoreactive levels in the adrenalectomized rat

To investigate the effects of type I (mineralocorticoid) and type II (glucocorticoid) receptor activation on striatal neuropeptide [preproenkephalin (PPE), preprotachykinin (PPT), and preprodynorphin (DYN)] mRNA and midbrain cholecystokinin (CCK) mRNA as well as striatal tyrosine hydroxylase radioimmunoreactivity (TH-RIC) levels, we administered either replacement levels of corticosterone (CORT; 0.5 mg/kg/day, s.c.) or pharmacological levels of deoxycorticosterone acetate (DOCA; a mineralocorticoid steroid with ability to bind to type I and type II receptors; 5 mg/kg, s.c.) to adrenalectomized adult male rats. After 1 week of recovery from adrenalectomy surgery, animals were injected daily with sesame oil or CORT for 1, 3, or 7 days or DOCA for 3 or 7 days and killed 16 h after the last injection. Adrenalectomy resulted in a decrease in all three striatal neuropeptide mRNA levels, compared with sham-operated rats. CORT replacement resulted in recovered PPE and PPT mRNA levels after 1 day and elevated PPE mRNA levels over those in sham-operated controls after 3 days. In contrast, DYN mRNA levels showed recovery after 7 days of CORT replacement. Results after DOCA treatment largely paralleled those after CORT replacement. There were no significant treatment effects on indirect markers of midbrain dopaminergic activity, i.e., CCK mRNA and TH-RIC. From these results we conclude that compared with striatal tachykinin and dynorphinergic neurons, enkephalinergic cells show greater sensitivity, whereas the dopaminergic system, including mesencephalic CCK, demonstrates an insensitivity to physiological CORT and to pharmacological DOCA treatment.     

Human 4-1BB regulates CD28 co-stimulation to promote Th1 cell responses

Our present study provides evidence that the 4-1BB signal is critical to CD28 co-stimulation in maintaining T cell activation when CD28 has been down-regulated because of repeated stimulation. The 4-1BB signal synergized with CD28 co-stimulation by lowering the threshold of anti-CD28 required to sustain proliferation and IL-2 production. The 4-1BB signal also modulated CD28-mediated cytokine profiles by markedly enhancing Th1 but suppressing Th2-type cytokine production. The 4-1BB signal generated Th1-type cells, as identified by intracellular IFN-gamma production. IFN-gamma induction was detected preferentially in 4-1BB-expressing cells, but not in those expressing CD30. 4-1BB and CD30 were induced in both CD4+ and CD8+ cells, but the location of the two molecules was mutually exclusive in each T cell subset. Our study suggests that the 4-1BB signal regulates CD28 co-stimulation in the targeted subset cells to favor Th1 development and maintain long-term cell growth.     

Structure and properties development in poly(phenylene sulfide) fibers. II. Effect of one-zone draw annealing

In this article, we discuss the role of one-zone drawing followed by annealing in enhancing the structure and properties of fibers manufactured from Fortron^® linear poly(phenylene sulfide) resins. The interaction effects of the polymer molecular weight (MW), melt-spinning process parameters, and draw-annealing process conditions were also elucidated. Several tools used to probe the investigation were tensile testing, differential scanning calorimetry, polarized light optical microscopy, wide-angle X-ray scattering, and small-angle X-ray scattering. This study showed that the optimum drawing temperature was around 95°C. A considerable improvement in the fiber tensile properties was observed upon drawing and annealing under optimum processing conditions. Fibers with tenacities close to 5 g/den were obtained. The development of the tensile properties was statistically correlated with the morphological changes in the fibers. The routes to achieving fibers with optimum tensile properties were shown to be different for resins with different MWs. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Pharmacokinetics of a synthetic, chemically modified hammerhead ribozyme against the rat cytochrome P-450 3A2 mRNA after single intravenous injections

Modulation of gene expression via nucleic acid sequence-specific intervention represents a new paradigm for drug discovery and development. Ribozymes are small RNA structures capable of cleaving RNA target molecules in a catalytic fashion. A 2'-O-allyl-modified hammerhead ribozyme designed to cleave the messenger RNA of cytochrome P-450 3A2 was administered to rats via 0.25 mg intravenous injections to investigate the disposition of this compound. The chemically modified ribozyme binds to serum albumin and can be displaced by phosphorothioate oligonucleotides. A biphasic plasma clearance with a distribution half-life of 12 min and an elimination half-life of 6.5 h was observed. A volume of distribution of 2.1 l/kg indicates perfusion into tissues well beyond the vascular system. The chemically modified ribozyme can be detected intact in the plasma up to 48 h after injection. Metabolic degradation of the chemically modified ribozyme occurs at unmodified ribonucleotides, leaving the 2'-O-allyl-modified sites intact. Recovery of intact chemically modified ribozyme was 1.9% of the administered dose at 12 h along with significant metabolites. The renal clearance of the intact ribozyme is an average 34.3 ml/h. The tissue distribution of the chemically modified ribozyme at 48 h is primarily to kidney and liver but the only detected material is a single 27-mer metabolite that has been cut in the unmodified GAAA region. The brain concentration of the prominent 27-mer metabolite is greater than that observed in the lung or spleen. Examination of tissues reveals no morphological evidence of toxicity. These data strongly support the potential utility of synthetic, 2'-O-allyl-modified hammerhead ribozymes as therapeutic agents in vivo.     

Serotonin modulation of sensory inputs to the lateral amygdala: dependency on corticosterone

The lateral nucleus of the amygdala (LA) receives excitatory (glutamatergic) inputs from thalamic and cortical sensory processing areas and is believed to be involved in evaluation of the affective significance of sensory events. We examined whether serotonin (5-HT) affects excitatory transmission in auditory afferents to the LA and, if so, whether this modulation of sensory transmission is regulated by the stress hormone corticosterone (CORT). Neuronal activity in the LA was elicited via iontophoretic ejection of L-glutamate or synaptically via electrical stimulation of auditory afferent pathways. In the intact rat, iontophoretically applied 5-HT inhibited both synaptically and glutamate-evoked action potentials in most neurons examined. However, after adrenalectomy (ADX), which eliminates endogenous CORT, 5-HT no longer inhibited evoked activity in the LA. High-CORT doses given to ADX animals reinstated the inhibition of excitatory transmission of 5-HT, whereas low-CORT doses had little effect. Immunocytochemical labeling of the glucocorticoid receptor in the intact rat demonstrated nuclear staining throughout several amygdala regions, including the LA. However, after ADX, no nuclear labeling was visible. With a high replacement dose of CORT (5 or 10 mg) after ADX, dense nuclear staining returned, but with a low replacement dose (1 mg/kg), there was only light nuclear staining. Thus, the ability of 5-HT to modulate glutamatergic activity in auditory pathways to the amygdala is dependent on the presence of CORT and possibly glucocorticoid activation. Via this mechanism, 5-HT modulates the processing of sensory information within the LA and thus may regulate amygdala-related functions.     

Cryogen spray cooling during Nd:YAG laser treatment of hemangiomas. A preliminary animal model study

BACKGROUND: Successful laser treatment of hemangiomas requires selective photothermal destruction of dilated cutaneous vessels without damaging the overlying epidermis. Delivering a short cryogen spurt, on the order of milliseconds, has been shown to result in localized cooling of the superficial skin structures during laser irradiation. OBJECTIVE: The purpose of this study was to examine the effectiveness of cryogen spray cooling (CSC) in protecting superficial tissue structures during continuous Nd:YAG laser irradiation of an in vivo model hemangioma. METHODS: The highly vascularized chicken comb was selected as the animal model for hemangiomas. The Nd:YAG laser irradiation ranged from 2.6 to 35.1 J/mm2. A feedback system utilizing infrared radiometry monitored the comb surface temperature and controlled delivery time of the cryogen spurt. When comb surface temperature during laser irradiation reached 36-42 degrees C, a 30-100 msec cryogen spurt was delivered. Animals were euthanized 1 hour to 21 days following each experiment. Gross and histologic analyses were performed. RESULTS: Nd:YAG laser irradiation resulted in deep (up to 6.1 mm) tissue photocoagulation, while CSC preserved the overlying epidermis and papillary dermis. CONCLUSION: The results demonstrate that CSC is effective in protecting the epidermis and papillary dermis, while achieving deep tissue photocoagulation during Nd:YAG laser irradiation. Further pilot studies in humans appear warranted.