Strutture a banda elettromagnetica proibita per la riduzione dell'accoppiamento mutuo

I moderni standard per la comunicazione wireless utilizzano la tecnologia Multiple Input Multiple Output (MIMO), che fa uso di più antenne, sia in trasmissione che in ricezione al fine di aumentare la capacità del canale. Nei dispositivi composti da più elementi radianti disposti sullo stesso substrato e posti a distanze di frazioni della lunghezza d’onda, si verificano problemi di accoppiamento tra le antenne che compongono la struttura; una della cause è lo stabilirsi delle onde superficiali che si propagano nella struttura. L’accoppiamento mutuo tra antenne comporta un innalzamento della correlazione tra i segnali ai morsetti delle antenne con conseguente riduzione delle prestazioni. Lo scopo di questo lavoro di tesi è quello di progettare particolari strutture che, sfruttando l’effetto di band gap elettromagnetico (EBG), inibiscano l’accoppiamento mediante le onde superficiali. Tali strutture potranno essere inserite tra antenne adiacenti sullo stesso substrato.ope

Combining Performance with Thermal Stability: Synthesis and Characterization of 5‐(3,5‐Dinitro‐1H‐pyrazol‐4‐yl)‐1H‐tetrazole and its Energetic Derivatives

In this study, we present the synthesis of 5‐(3,5‐dinitro‐1H‐pyrazol‐4‐yl)‐1H‐tetrazole and its energetic derivatives starting from 4‐amino‐3,5‐dinitropyrazole, which was diazotized and cyanide substituted. A subsequent cycloaddition reaction with sodium azide led to 5‐(3,5‐dinitro‐1H‐pyrazol‐4‐yl)‐1H‐tetrazole (3). Several alkaline metal and nitrogen‐rich salts were prepared and characterized by low‐temperature X‐ray diffraction. Additionally, all compounds were analyzed by vibrational spectroscopy (IR), 1H, 13C and 14N NMR spectroscopy, elemental analysis and differential thermal analysis (DTA). Additionally, the heats of formation for selected compounds were calculated using the atomization method based on CBS‐4M enthalpies as well as important detonation parameters by using the EXPLO5 code (V6.05). Furthermore, the sensitivities of 3 and all synthesized salts toward friction, impact and electrostatic discharge according to BAM (Bundesamt für Materialforschung) were determined and compared to RDX

Preliminary investigation of blood vessel-derived acellular matrix for vascular graft application

Although autologous vascular grafts and artificial materials have been used for reconstruction of small diameter (<5mm) blood vessels, the poor availability of vessels and the occurrence of intimal hyperplasia and progressive atherosclerotic degeneration represent shortcomings of these vascular prostheses. Therefore, this preliminary study aimed to develop acellular matrix (AM)-based vascular grafts. Rat thoracic aortas were decellularized by means of a detergent-enzymatic treatment [1], whereas endothelial cells (ECs) were obtained through enzymatic digestion of rat skin followed by immunomagnetic separation of CD31-positive cells. Twenty male Lewis rats (8 week old) received either only AM and previously in vitro reendothelized AM as abdominal aorta Interposition grafts (about 2 cm). After 1 (n=10) and 3 (n=10) months from surgery, grafts were explanted and morphologically examined by scanning electron microscopy and Movat staining. The detergent enzymatic treatment completely removed the cellular part of vessels and both MHC class I and class II antigens. After 1 month from surgery, the luminal surface of implanted AMs was partially covered by ECs and several platelets adhered in the areas lacking cell coverage. Intimal hyperplasia, already detected after 1 month, increased at 3 months. On the contrary, all the grafts composed by AM and ECs were completely covered at 1 month and their structure was similar to that of native vessels at 3 months. Taken together, our findings show that prostheses composed of AM pre-seeded with ECs could be a promising approach for the replacement of blood vessels

Role of enzymatic activity inmuscle damage and cytotoxicity induced by Bothrops asper Asp49 phospholipase A2 myotoxins: are there additional effector mechanisms involved?

artículo (arbitrado) -- Universidad de Costa Rica, Instituto de Investigaciones Clodomiro Picado (ICP). 2014Viperid venoms often contain mixtures of Asp49 and Lys49 PLA2 myotoxin isoforms, relevant to development of myonecrosis. Given their difference in catalytic activity, mechanistic studies on each type require highly purified samples. Studies on Asp49 PLA2s have shown that enzyme inactivation using p-bromophenacyl bromide (p-BPB) drastically affects toxicity. However, based on the variable levels of residual toxicity observed in some studies, it has been suggested that effector mechanisms independent of catalysis may additionally be involved in the toxicity of these enzymes, possibly resembling those of the enzymatically inactive Lys49 myotoxins. A possibility that Lys49 isoforms could be present in Asp49 PLA2 preparations exists and, if undetected in previous studies, could explain the variable residual toxicity. This question is here addressed by using an enzyme preparation ascertained to be free of Lys49 myotoxins. In agreement with previous reports, inactivation of the catalytic activity of an Asp49 myotoxin preparation led to major inhibition of toxic effects in vitro and in vivo. The very low residual levels of myotoxicity (7%) and cytotoxicity (4%) observed can be attributed to the low, although detectable, enzyme remaining active after p-BPB treatment (2.7%), and would be difficult to reconcile with the proposed existence of additional catalytic-independent toxic mechanisms. These findings favor the concept that the effector mechanism of toxicity of Asp49 PLA2 myotoxins from viperids fundamentally relies on their ability to hydrolyze phospholipids, arguing against the proposal that membrane disruption may also be caused by additional mechanisms that are independent of catalysis.International Centre for Genetic Engineering and Biotechnology (ICGEB, Italy; CRP/COS13-01); Vicerrectorıa de Investigacion (UCR; 741-B4-100). Sistema de Estudios de Posgrado, Universidad de Costa Rica (SEP-UCR).UCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias de la Salud::Instituto Clodomiro Picado (ICP

Sphingomyelinase D Activity in Model Membranes: Structural Effects of in situ Generation of Ceramide-1-Phosphate

The toxicity of Loxosceles spider venom has been attributed to a rare enzyme, sphingomyelinase D, which transforms sphingomyelin to ceramide-1-phosphate. The bases of its inflammatory and dermonecrotic activity, however, remain unclear. In this work the effects of ceramide-1-phosphate on model membranes were studied both by in situ generation of this lipid using a recombinant sphingomyelinase D from the spider Loxosceles laeta and by pre-mixing it with sphingomyelin and cholesterol. The systems of choice were large unilamellar vesicles for bulk studies (enzyme kinetics, fluorescence spectroscopy and dynamic light scattering) and giant unilamellar vesicles for fluorescence microscopy examination using a variety of fluorescent probes. The influence of membrane lateral structure on the kinetics of enzyme activity and the consequences of enzyme activity on the structure of target membranes containing sphingomyelin were examined. The findings indicate that: 1) ceramide-1-phosphate (particularly lauroyl ceramide-1-phosphate) can be incorporated into sphingomyelin bilayers in a concentration-dependent manner and generates coexistence of liquid disordered/solid ordered domains, 2) the activity of sphingomyelinase D is clearly influenced by the supramolecular organization of its substrate in membranes and, 3) in situ ceramide-1-phosphate generation by enzymatic activity profoundly alters the lateral structure and morphology of the target membranes

Calcium plays a key role in the effects induced by a snake venom Lys49 phospholipase A2 homologue on a lymphoblastoid cell line

A catalytically-inactive Lys49 phospholipase A2 homologue from the venom of the snake Bothrops asper induces diverse effects (necrosis, apoptosis and proliferation) in a lymphoblastoid cell line, depending on the toxin concentration. The increments in cytosolic Ca2+ levels induced by this toxin in this cell line were assessed. At high toxin concentration (100 microg/mL) the toxin induces drastic disruption of the plasma membrane, associated with a prominent Ca2+ influx and necrosis. Previous incubation of the cells with the chelating agent EGTA or with ruthenium red, an inhibitor of the uniporter mitochondrial Ca2+ transport, greatly reduced necrosis. At a toxin concentration of 12.5 microg/mL, apoptosis is the predominant response, being associated with lower increments in cytosolic Ca2+. This effect was inhibited by preincubation with ruthenium red and the cytosolic Ca2+ chelator BAPTA-AM. The proliferative response, which occurs at a low toxin concentration (0.5 microg/mL), is associated with a small and oscillatory increment in cytosolic Ca2+. It was inhibited by EGTA, ruthenium red and BAPTA-AM, by inhibitors of the endoplasmic reticulum Ca2+ -ATPase (SERCA) and by blockade of the ryanodine receptor. It is concluded that necrosis and apoptosis induced by this toxin are associated with increments in cytosolic Ca2+ levels following plasma membrane perturbation, together with the involvement of mitochondria. The cellular proliferative response depends on a limited Ca2+ influx through the plasma membrane, being associated with a concerted functional unit constituted by SERCA, the ryanodine receptor and mitochondria, which regulate the observed oscillations in cytosolic Ca2+ concentration.Universidad de Costa Rica//UCR/Costa RicaUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias de la Salud::Instituto Clodomiro Picado (ICP

Experimental pathology of local tissue damage induced by Bothrops asper snake venom

Envenomations by Bothrops asper are often associated with complex and severe local pathological manifestations, including edema, blistering, dermonecrosis, myonecrosis and hemorrhage. The pathogenesis of these alterations has been investigated at the experimental level. These effects are mostly the consequence of the direct action of zinc-dependent metalloproteinases (SVMPs) and myotoxic phospholipases A2 (PLA2s). SVMPs induce hemorrhage, blistering, dermonecrosis and general extracellular matrix degradation, whereas PLA2s induce myonecrosis and also affect lymphatic vessels. In addition, the prominent vascular alterations leading to hemorrhage and edema may contribute to ischemia and further tissue necrosis. The mechanisms of action of SVMPs and PLA2s are discussed in detail in this review. Venom-induced tissue damage plays also a role in promoting bacterial infection. A prominent inflammatory reaction develops as a consequence of these local pathological alterations, with the synthesis and release of abundant mediators, resulting in edema and pain. However, whether inflammatory cells and mediators contribute to further tissue damage is not clear at present. Muscle tissue regeneration after venom-induced pathological effects is often impaired, thus resulting in permanent tissue loss and dysfunction. SVMP-induced microvessel damage is likely to be responsible of this poor regenerative outcome. Antivenoms are only partially effective in the neutralization of B. asper-induced local effects, and the search for novel toxin inhibitors represents a potential avenue for improving the treatment of this serious aspect of snakebite envenomation.UCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias de la Salud::Instituto Clodomiro Picado (ICP

Synergism between basic Asp49 and Lys49 phospholipase A2 myotoxins of viperid snake venom in vitro and in vivo

artículo (arbitrado) -- Universidad de Costa Rica, Instituto de investigaciones Clodomiro Picado. 2014Two subtypes of phospholipases A2 (PLA2s) with the ability to induce myonecrosis, ‘Asp49’ and ‘Lys49’ myotoxins, often coexist in viperid snake venoms. Since the latter lack catalytic activity, two different mechanisms are involved in their myotoxicity. A synergism between Asp49 and Lys49 myotoxins from Bothrops asper was previously observed in vitro, enhancing Ca2+ entry and cell death when acting together upon C2C12 myotubes. These observations are extended for the first time in vivo, by demonstrating a clear enhancement of myonecrosis by the combined action of these two toxins in mice. In addition, novel aspects of their synergism were revealed using myotubes. Proportions of Asp49 myotoxin as low as 0.1% of the Lys49 myotoxin are sufficient to enhance cytotoxicity of the latter, but not the opposite. Sublytic amounts of Asp49 myotoxin also enhanced cytotoxicity of a synthetic peptide encompassing the toxic region of Lys49 myotoxin. Asp49 myotoxin rendered myotubes more susceptible to osmotic lysis, whereas Lys49 myotoxin did not. In contrast to myotoxic Asp49 PLA2, an acidic non-toxic PLA2 from the same venom did not markedly synergize with Lys49 myotoxin, revealing a functional difference between basic and acidic PLA2 enzymes. It is suggested that Asp49 myotoxins synergize with Lys49 myotoxins by virtue of their PLA2 activity. In addition to the membrane-destabilizing effect of this activity, Asp49 myotoxins may generate anionic patches of hydrolytic reaction products, facilitating electrostatic interactions with Lys49 myotoxins. These data provide new evidence for the evolutionary adaptive value of the two subtypes of PLA2 myotoxins acting synergistically in viperid venoms.Funding support by the Graduate Studies Program, Universidad de Costa Rica; International Centre for Genetic Engineering and Biotechnology, Italy (CRP/COS13-01); and Vicerrectoria de Investigacion, Universidad de Costa Rica (741-B4-100).UCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias de la Salud::Instituto Clodomiro Picado (ICP