Improvement of the 3ω\omega thermal conductivity measurement technique at nanoscale

The reduction of the thermal conductivity in nanostructures opens up the possibility of exploiting for thermoelectric purposes also materials such as silicon, which are cheap, available and sustainable but with a high thermal conductivity in their bulk form. The development of thermoelectric devices based on these innovative materials requires reliable techniques for the measurement of thermal conductivity on a nanometric scale. The approximations introduced by conventional techniques for thermal conductivity measurements can lead to unreliable results when applied to nanostructures, because heaters and temperature sensors needed for the measurement cannot have a negligible size, and therefore perturb the result. In this paper we focus on the 3$\omega$ technique, applied to the thermal conductivity measurement of suspended silicon nanomembranes. To overcome the approximations introduced by conventional analytical models used for the interpretation of the 3$\omega$ data, we propose to use a numerical solution, performed by means of finite element modeling, of the thermal and electrical transport equations. An excellent fit of the experimental data will be presented, discussed, and compared with an analytical model

Thermal conductivity of silicon nanowire forests

A large amount of parallel silicon nanowires, placed perpendicularly to a silicon substrate (silicon nanowire forests), have been contacted and assembled in order to fabricate legs of a thermoelectric generator. This paper reports the measurement of the main parameter for thermoelectric applications, which is the thermal conductivity. The reported value, which confirms the strong reduction of the thermal conductivity in nanostructures, is measured on a large amount (>107) of parallel nanowires with a diameter variable in the range 60-120 nm, and takes into account eventual non-uniformities which are unavoidable on surfaces of several mm2. As silicon nanowire forests are very thin, it has been necessary to develop a suitable measurement apparatus. The fabrication of devices based on silicon nanowire forests, the apparatus and the measurement procedure, as well as the the results, are illustrated and discussed

Interaction of glutathione transferase from horse erythrocytes with 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole

7-Chloro-4-nitrobenzo-2-oxa-1,3-diazole reacts with two thiol groups of the dimeric horse erythrocyte glutathione transferase at pH 5.0, with strong inactivation reversible on dithiothreitol treatment. The inactivation kinetic follows a biphasic pattern, similar to that caused by other thiol reagents as recently reported. Both S-methylglutathione and 1-chloro-2,4-dinitrobenzene protect the enzyme from inactivation. Analysis of the reactive SH group-containing peptide gives the sequence Ala-Ser-Cys-Leu-Tyr, identical with that of the peptide that contains the reactive cysteine 47 of the human placental transferase. In the presence of glutathione, the enzyme is not inactivated by this reagent, but it catalyzes its conjugation to glutathione. At higher pH values, 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole reacts with 2 tyrosines/dimer and lysines, as well as with cysteines. Reaction with lysine seems essentially without effect on activity; whether the reactive tyrosines are important for activity could not be determined using this reagent only. However, 2 tyrosines among the 4 that are nitrated by tetranitro-methane are important for activity

Occurrence of pathogenic and faecal Escherichia coli in layer hens

A total of 117 Escherichia coli from colibacillosis affected (APEC) and clinically healthy birds (AFEC) were serotyped and tested for the presence of virulence genes: iss, tsh, cva. A total of 54.5% E. Coli were typeable and 15 different serogroups were identified. The most common serogroups among APEC strains were O78, O2 and O128, whereas O139 was predominant in faecal strains from healthy birds. Iss, tsh e cva were more frequently detected among the septicaemic E. coli strains. The association of virulence genes was observed. Particularly, the pathotype iss-tsh-cva was present in 46.5% of APEC strains. Referring to serogroups, E. coli O78 and O2 originating from colibacillosis affected birds were always isstsh- cva positive but did not share virulence genes when they came from healthy birds

Avian Pathogenic Escherichia coli in Audouin gulls (Larus audouinii) Could they affect the surviving of the bird colonies

A total of 39 E. coli strains isolated from cloacal swabs and unhatched eggs of Audouin's gulls (Larus audouinii) living the Salento coast (Italy) were serotyped and molecular characterized for the presence of irp2, fyuA, tsh, papC, fimC, iucD, and eae genes described for Avian Pathogenic E. coli (APEC). Eight different serogroups (O1, 06, 08, 015, 075, 0139, 0146, 0147) were distinguished: we recorded a very high rate of untypeable strains. Genotyping by PCR achieved to detect fimC and irp2, described for APEC strains, as most predominant genes circulating in the gulls population, accounting for 94.87% and 97.43% respectively. Nevertheless, a significant co-existance of virulence genes was demonstrated to belong to E.coli of eggs origin. Particularly, fimC/tsh/iucD pathotype, recognized as most responsible of illness in poultry, emerged in 8.69% of E. coli of eggs origin

Bilateral synovial chondromatosis of the first metatarsophalangeal joint: a report case

Synovial chondromatosis is a rare pathology of unknown aetiology. It originates from the chondroid metaplasia of the connective tissue of the synovial membrane. Consequently, cartilaginous nodules develop in the affected joints, first calcifying and then ossifying. The bursae mucosae, the vaginae tendinis and the para-articular connective tissue are less frequently affected. The most common locations of this pathology are the knee, the hip, the shoulder, the elbow and the ankle. The small articulations are rarely affected, even less the bilateral involving of joints, above all of hand or foot, is exceptional. In a clinical and radiological valuation, it is difficult to distinguish synovial chondromatosis from arthrosis and from degenerative arthopathies in general. A sure diagnosis can be obtained only by means of a histological examination. We here report a case of synovial chondromatosis bilaterally located on the first metatarsophalangeal joint. Clinical and radiological features were analogous to those of hallux rigidus, a typical and peculiar metatarsophalangeal joint pathology. The diagnostic suspicion that it was a synovial chondromatosis arose during surgical surgery, and was subsequently confirmed by histological examination. During the following visits, the patient did not present any painful symptomatology

Selective organic functionalization of polycrystalline silicon-germanium for bioMEMS applications

AbstractWe selectively immobilized organofunctional silanes on top of polycrystalline silicon-germanium (poly-SiGe) layers, as a first step towards the fabrication of poly-SiGe-based bioMEMS (biomedical MicroElectroMechanicalSystems) by means of standard UV photolithography. 3-aminopropyl-dimethyl-ethoxysilane (APDMES) and 3-aminopropyl-triethoxysilane (APTES) molecules were immobilized onto resist-patterned poly-SiGe surfaces. The protocols for surface hydroxylation and silane immobilization were designed to be CMOS-compatible and to avoid damage to photoresist. Silanized surfaces were investigated both by means of fluorescence microscopy, and by FEG-SEM observation after labeling with 30 nm-diameter gold nanoparticles (NPs). We report the silanization protocols, together with the results indicating successful organic functionalization of the samples

Nanostructured potential well/barrier engineering for realizing unprecedentedly large thermoelectric power factors

This work describes, through the semi-classical Boltzmann transport theory and simulation, a novel nanostructured material design that can lead to unprecedentedly high thermoelectric power factors, with improvements of more than an order of magnitude compared to optimal bulk material power factors. The design is based on a specific grain/grain-boundary (potential well/barrier) engineering such that: i) carrier energy filtering is achieved using potential barriers, combined with ii) higher than usual doping operating conditions such that high carrier velocities and mean-free-paths are utilized, iii) minimal carrier energy relaxation is achieved after passing over the barriers to propagate the high Seebeck coefficient of the barriers into the potential wells, and, importantly, iv) an intermediate dopant-free (depleted) region is formed. Thus, the design consists of a ‘three-region geometry’, in which the high doping resides in the center/core of the potential well, with a dopant-depleted region separating the doped region from the potential barriers. It is shown that the filtering barriers are optimal when they mitigate the reduction in conductivity they introduce, and this can be done primarily when they are ‘clean’ from dopants during the process of filtering. The potential wells, on the other hand, are optimal when they mitigate the reduced Seebeck coefficient they introduce by: i) not allowing carrier energy relaxation, and ii) mitigating the reduction in mobility that the high concentration of dopant impurities causes. It is shown that dopant segregation, with ‘clean’ dopant-depletion regions around the potential barriers, serves this key purpose of improved mobility toward the phonon-limited mobility levels in the wells. Using quantum transport simulations based on the non-equilibrium Green's function method as well as semi-classical Monte Carlo simulations, we also verify the important ingredients and validate this ‘clean-filtering’ design