Unexpected Scaling of the Performance of Carbon Nanotube Transistors

We show that carbon nanotube transistors exhibit scaling that is qualitatively different than conventional transistors. The performance depends in an unexpected way on both the thickness and the dielectric constant of the gate oxide. Experimental measurements and theoretical calculations provide a consistent understanding of the scaling, which reflects the very different device physics of a Schottky barrier transistor with a quasi-one-dimensional channel contacting a sharp edge. A simple analytic model gives explicit scaling expressions for key device parameters such as subthreshold slope, turn-on voltage, and transconductance.Comment: 4 pages, 4 figure

Izolacija i karakterizacija bakterijske flore iz autohtonih fermentisanih proizvoda Srbije i Crne Gore

The natural community of lactic acid bacteria isolated from farmhouse fermented milk products has been investigated. In such products, where no starters are added, fermentation occurs as a result of natural flora present in the surrounding environment. A total of 200 isolated strains were examined for their acidification activity and EPS formation. Out of the 200 isolated strains, 27 strains were selected for further investigation. They were further identified by 16S rRNA sequencing in order to obtain the identification at species level, which showed that 14 strains belong to Lactococcus lactis subsp. lactis, 10 of them to Lactobacillus sp and 3 strains belongs to Leuconostoc sp. To differentiate between strains the pulsed-field gel electrophoresis (PFGE) patterns, of 15 isolated lactococcal strains, was generated using Smal or Ascl. Unrelated strains yielded different patterns of digestion products. The plasmid isolation of these strains has also been conducted in order to compare these results to patterns of PFGE. Phage typing of the Lactococcus sp. strains has been conducted. All lactococcal strains were resistant against 41 phages (Chr. Hansen phage collection) representing the major phage groups known for Lactococcus. These results indicate that the strains represent a possible tool for cultures that have not been exposed to any industrial selection.U ovom radu su proučavani sojevi bakterija mlečne kiseline izolovani iz autohtonih fermentisanih mlečnih proizvoda. Kod ovih proizvoda, kojima se ne dodaju starter kulture, fermentacija se odigrava kao rezultat aktivnosti prirodne mikroflore koja je prisutna u okolnoj sredini. Kod ukupno 200 sojeva proučavana je njihova sposobnost acidifikacije i sposobnost stvaranja egzopolisaharida (EPS). Od ukupno 200 izolovanih sojeva selektovano je njih 27 koji su podvrgnuti daljem proučavanju. Nakon ove selekcije, sojevi su identifikovani 16S rRNA sekvenciranjem u cilju njihove identifikacije na nivou vrste. Od 27 selektovanih sojeva, 14 je pripadalo vrsti Lactococcus lactis subsp. Lactis, 3 soja je pripadalo vrsti Leuconostoc spp., dok je 10 sojeva pripadalo vrsti Lactobacillus sp. Da bi se utvrdile razlike između različitih sojeva urađena je analiza uz korišćenje elektroforeze u pulsirajućem električnom polju (PFGE), a matrice su dobijene uz korišćenje Smal i AscI restrikcionih enzima. Sojevi koji nisu u srodstvu dali su različite matrice digestionih produkata. Izvršena je i izolacija plazmida iz ovih sojeva kako bi se potvrdili rezultati dobijeni PFGE tehnikom. Takođe je izvršena i fagotipizacija sojeva za sve sojeve za koje je dokazano da pripadaju vrsti Lactococcus sp. Svi laktokokni sojevi su bili rezistentni na 41 fag (kolekcija faga kompanije Chr. Hansen) koji predstavljaju grupu bakteriofaga koji su najčešći za vrstu Lactococcus. Dobijeni rezultati ukazuju na to da proučavani sojevi predstavljaju mogući izvor kultura koji do sada nisu bili izloženi bilo kakvoj industrijskoj selekciji

Checks and Balances in Autoimmune Vasculitis

Age-associated changes in the immune system including alterations in surface protein expression are thought to contribute to an increased susceptibility for autoimmune diseases. The balance between the expression of coinhibitory and costimulatory surface protein molecules, also known as immune checkpoint molecules, is crucial in fine-tuning the immune response and preventing autoimmunity. The activation of specific inhibitory signaling pathways allows cancer cells to evade recognition and destruction by the host immune system. The use of immune checkpoint inhibitors (ICIs) to treat cancer has proven to be effective producing durable antitumor responses in multiple cancer types. However, one of the disadvantages derived from the use of these agents is the appearance of inflammatory manifestations termed immune-related adverse events (irAEs). These irAEs are often relatively mild, but more severe irAEs have been reported as well including several forms of vasculitis. In this article, we argue that age-related changes in expression and function of immune checkpoint molecules lead to an unstable immune system, which is prone to tolerance failure and autoimmune vasculitis development. The topic is introduced by a case report from our hospital describing a melanoma patient treated with ICIs and who subsequently developed biopsy-proven giant cell arteritis. Following this case report, we present an in-depth review on the role of immune checkpoint pathways in the development and progression of autoimmune vasculitis and its relation with an aging immune system

Spin dynamics of the S=1/2 antiferromagnetic zig-zag ladder with anisotropy

We use exact diagonalization and the modified Lanczos method to study the finite energy and finite momentum spectral weight of the longitudinal and transverse spin excitations of the anisotropic zig-zag ladder. We find that the spin excitations form continua of gapless or gapped spinons in the different regions of the phase diagram. The results obtained are consistent with a picture previously proposed that in the anisotropic case there is a transition from a gapped regime to a gapless regime, for small interchain coupling. In this regime we find a sharp low-energy peak in the structure function for the transverse spin excitations, consistent with a finite stiffness.Comment: 17 figure

Scaling analysis of Schottky barriers at metal-embedded semiconducting carbon nanotube interfaces

We present an atomistic self-consistent tight-binding study of the electronic and transport properties of metal-semiconducting carbon nanotube interfaces as a function of the nanotube channel length when the end of the nanotube wire is buried inside the electrodes. We show that the lineup of the nanotube band structure relative to the metal Fermi-level depends strongly on the metal work function but weakly on the details of the interface. We analyze the length-dependent transport characteristics, which predicts a transition from tunneling to thermally-activated transport with increasing nanotube channel length.Comment: To appear in Phys.Rev.B Rapid Communications. Color figures available in PRB online versio

Helix vs. Sheet Formation in a Small Peptide

Segments with the amino acid sequence EKAYLRT appear in natural occurring proteins both in $\alpha$-helices and $\beta$-sheets. For this reason, we have use this peptide to study how secondary structure formation in proteins depends on the local environment. Our data rely on multicanonical Monte Carlo simulations where the interactions among all atoms are taken into account. Results in gas phase are compared with that in an implicit solvent. We find that both in gas phase and solvated EKAYLRT forms an $\alpha$-helix when not interacting with other molecules. However, in the vicinity of a $\beta$-strand, the peptide forms a $\beta$-strand. Because of this change in secondary structure our peptide may provide a simple model for the $\alpha \to \beta$ transition that is supposedly related to the outbreak of Prion diseases and similar illnesses.Comment: to appear in Physical Review

Decoupling of the S=1/2 antiferromagnetic zig-zag ladder with anisotropy

The spin-1/2 antiferromagnetic zig-zag ladder is studied by exact diagonalization of small systems in the regime of weak inter-chain coupling. A gapless phase with quasi long-range spiral correlations has been predicted to occur in this regime if easy-plane (XY) anisotropy is present. We find in general that the finite zig-zag ladder shows three phases: a gapless collinear phase, a dimer phase and a spiral phase. We study the level crossings of the spectrum,the dimer correlation function, the structure factor and the spin stiffness within these phases, as well as at the transition points. As the inter-chain coupling decreases we observe a transition in the anisotropic XY case from a phase with a gap to a gapless phase that is best described by two decoupled antiferromagnetic chains. The isotropic and the anisotropic XY cases are found to be qualitatively the same, however, in the regime of weak inter-chain coupling for the small systems studied here. We attribute this to a finite-size effect in the isotropic zig-zag case that results from exponentially diverging antiferromagnetic correlations in the weak-coupling limit.Comment: to appear in Physical Review

Carbon Nanotube Field-Effect Transistors With Integrated Ohmic Contacts and High-k Gate Dielectrics

High performance enhancement mode semiconducting carbon nanotube field-effect transistors (CNTFETs) are obtained by combining ohmic metal-tube contacts, high dielectric constant HfO2 films as gate insulators, and electrostatically doped nanotube segments as source/drain electrodes. The combination of these elements affords high ON currents, subthreshold swings of ~ 70-80 mV/decade, and allows for low OFF currents and suppressed ambipolar conduction. The doped source and drain approach resembles that of MOSFETs and can impart excellent OFF states to nanotube FETs under aggressive vertical scaling. This presents an important advantage over devices with metal source/drain, or devices commonly referred to as Schottky barrier FETs