Catalytic RNA and synthesis of the peptide bond

We are studying whether the L-19 IVS ribozyme from Tetrahymena thermophila can catalyze the formation of the peptide bond when it is supplied with synthetic aminoacyl oligonucleotides. If this reaction works, it could give us some insight into the mechanism of peptide bond formation and the origin of coded protein synthesis. Two short oligoribonucleotides, CCCCC and a protected form of CCCCU were prepared; the former was made by the controlled hydrolysis of Poly(C), and the later by multistep chemical synthesis from the protected monomers. The homopentamer was then aminocylated using C-14 labelled Boc-protected glycine imidazolide. This aminoacylated oligo-nucleotide has now been shown to enter the active site of the L-19 IVS, and aminoacyl transfer, and peptide bond formation reactions are being sought. Our synthesis of CCCCU made us aware of the inadequacy of many of the 2'- hydroxyl protecting groups that are in use today and we therefore designed a new 2'- protecting group that is presently being tested

Quantum Hall induced currents and the magnetoresistance of a quantum point contact

We report an investigation of quantum Hall induced currents by simultaneous measurements of their magnetic moment and their effect on the conductance of a quantum point contact (QPC). Features in the magnetic moment and QPC resistance are correlated at Landau-level filling factors nu=1, 2 and 4, which demonstrates the common origin of the effects. Temperature and non-linear sweep rate dependences are observed to be similar for the two effects. Furthermore, features in the noise of the induced currents, caused by breakdown of the quantum Hall effect, are observed to have clear correlations between the two measurements. In contrast, there is a distinct difference in the way that the induced currents decay with time when the sweeping field halts at integer filling factor. We attribute this difference to the fact that, while both effects are sensitive to the magnitude of the induced current, the QPC resistance is also sensitive to the proximity of the current to the QPC split-gate. Although it is clearly demonstrated that induced currents affect the electrostatics of a QPC, the reverse effect, the QPC influencing the induced current, was not observed

Colloquium: Physics of optical lattice clocks

Recently invented and demonstrated, optical lattice clocks hold great promise for improving the precision of modern timekeeping. These clocks aim at the 10^-18 fractional accuracy, which translates into a clock that would neither lose or gain a fraction of a second over an estimated age of the Universe. In these clocks, millions of atoms are trapped and interrogated simultaneously, dramatically improving clock stability. Here we discuss the principles of operation of these clocks and, in particular, a novel concept of "magic" trapping of atoms in optical lattices. We also highlight recently proposed microwave lattice clocks and several applications that employ the optical lattice clocks as a platform for precision measurements and quantum information processing.Comment: 18 pages, 15 figure

High-voltage MOSFET bipolar square-wave generator

he construction of a high‐voltage (up to 1000 V) bipolar metal‐oxide‐semiconductor field‐effect transistor square‐wave generator is described. This generator is capable of producing both positive and negative going square waves with variable amplitude, repetition rate, and width. The circuit was designed for ferroelectrics research, however other applications are possible. The rise time of the prototype was 200 ns which was quite satisfactory for the present ferroelectric research project however the rise time can be decreased to 50 ns if necessary. The reader with a modest knowledge of electronics should be able to construct the circuit. Possible pitfalls and critical points are discussed

Comparing verbal media for alarm handling: Speech versus textual displays

The rise of computers in command and control domains has meant that control operations can be performed via desk-based visual display terminals. This trend has also produced the potential to display information to operators in a variety of formats. Of particular interest has been the use of text-based displays for alarm presentation. There are possible limitations to the use of text for alarm presentation, not least of which is the need for a dedicated alarms display screen (or, at least, a display page). Given the capability of computers to synthesize speech, it is possible that speech-based alarms could generate the same information as text-based displays without the need for dedicated screen space. In this paper an experimental comparison of speech-based and text-based displays for presentation of alarms is reported. The findings show that speech leads to longer response times than text displays, but that it has minimal effect on the efficacy of fault handling. The results are discussed within the alarm initiated activities framework and implications for alarm system design are outlined

Search strategies for supermassive stars in young clusters and application to nearby galaxies

Supermassive stars (SMS) with masses $M \gtrsim 10^3-10^4 M_{\odot}$, formed by runaway collisions in young, massive, and dense star clusters have been invoked as a possible solution to the puzzles raised by the presence of multiple stellar populations and peculiar abundance patterns observed in globular clusters. However, such objects have not been observed so far. We developed observational strategies to search for SMS hosted within young massive clusters (thought to be the precursors of globular clusters, GCs), which could be applicable in a relatively general fashion, using both photometric and spectroscopic observations. We used theoretical predictions of spectra of SMS and SMS-hosting clusters, together with predictions from standard simple stellar populations to examine their impact on color-color diagrams and on individual optical spectral lines (primarily Hydrogen emission and absorption lines). As a first step, we apply our search strategies to a sample of $\sim 3000$ young star clusters (YSC) from two nearby galaxies with multi-band observations from the HST and optical integral-field spectroscopy obtained with MUSE on the Very Large Telescope. We focus on models for SMS with large radii (corresponding to $Teff \lesssim 7000$ K), which predict strong Balmer breaks, and construct proper color-color diagrams to select the corresponding SMS-hosting cluster candidates. We show that their spectrophotometric properties are similar to that of normal clusters with ages of a few hundred Myr, which would, however, show signs of composite stellar populations, in particular the presence of nebular lines (H${\alpha}$ and others). Examining the photometry, overall SEDs, and the spectra of $\sim 100$ clusters with strong Balmer breaks, we have found several objects with peculiar SEDs, the presence of emission lines, or other peculiar signatures. [abridged]Comment: Accepted for publication in A&A, 15 pages, 12 figures, 2 tables, (Abstract abridged

Risk Prediction Models for Colorectal Cancer: A Systematic Review.

Colorectal cancer is the second leading cause of cancer-related death in Europe and the United States. Survival is strongly related to stage at diagnosis and population-based screening reduces colorectal cancer incidence and mortality. Stratifying the population by risk offers the potential to improve the efficiency of screening. In this systematic review we searched Medline, EMBASE, and the Cochrane Library for primary research studies reporting or validating models to predict future risk of primary colorectal cancer for asymptomatic individuals. A total of 12,808 papers were identified from the literature search and nine through citation searching. Fifty-two risk models were included. Where reported (n = 37), half the models had acceptable-to-good discrimination (the area under the receiver operating characteristic curve, AUROC >0.7) in the derivation sample. Calibration was less commonly assessed (n = 21), but overall acceptable. In external validation studies, 10 models showed acceptable discrimination (AUROC 0.71-0.78). These include two with only three variables (age, gender, and BMI; age, gender, and family history of colorectal cancer). A small number of prediction models developed from case-control studies of genetic biomarkers also show some promise but require further external validation using population-based samples. Further research should focus on the feasibility and impact of incorporating such models into stratified screening programmes.J Usher-Smith is funded by a National Institute of Health Research (NIHR) Clinical Lectureship and F Walter by an NIHR Clinician Scientist award. J Emery is funded by an Australian National Health and Medical Research Council (NHMRC) Practitioner Fellowship. A Wong has an NHMRC Early Career Fellowship. The views expressed in this publication are those of the authors and not necessarily those of the NHS, the NIHR or the Department of Health.This is the author accepted manuscript. The final version is available from American Association for Cancer Research via http://dx.doi.org/10.1158/1940-6207.CAPR-15-027

Magnetization Measurements of High-Mobility Two-Dimensional Electron Gases

De Haas–van Alphen (dHvA) oscillations are observed for Landau levels (LLs) with filling factors between 4 and 52, at temperatures in the range 50 mK to 1 K, in experiments on high-mobility GaAs/(Al, Ga)As heterojunctions. The oscillations become sawtooth-shaped at low filling factors, and theoretical fits to the data, assuming the two-dimensional electron gas to be a non-interacting Fermi system, show the shape of LLs to be close to a δ function. The small residual width (∼0.4 meV or less) fits equally well to either a Gaussian or a Lorentzian density-of-states model. In almost all cases, a constant background density of states has to be included to obtain a satisfactory fit. Weak odd-filling-factor dHvA peaks are detected at high fields, from which a g-factor enhancement of 15 can be inferred. Comparison of the scattering time derived from the fits before and after illumination, with the momentum relaxation time derived from transport, reveals a counterintuitive behavior in the bulk-modulation-doped sample

Magnetization measurements of high-mobility two-dimensional electron gases

De Haas-van Alphen (dHvA) oscillations are observed for Landau levels (LLs) with filling factors between 4 and 52, at temperatures in the range 50 mK to 1 K, in experiments on high mobility GaAs/(Al, Ga)As heterojunctions. The oscillations become sawtooth-shaped at low filling factors, and theoretical fits to the data, assuming the two-dimensional electron gas to be a non-interacting Fermi system, show the shape of LLs to be close to a ?-function. The small residual width (~0.4 meV or less) fits equally well to either a Gausian or a Lorentzian density of states model. In almost all cases, a constant background density of states has to be included to obtain a satisfactory fit. weak odd-filling-factor dHvA peaks are detected at high fields, from which a g-factor enhancement of 15 can be inferred. Comparison of the scattering time derived from the fits before and after illumination, with the momentum relaxation time derived from transport, reveals a counterintuitive behavior in the bulk-modulation-doped sample

Universal Prefactor of Activated Conductivity in the Quantum Hall Effect

The prefactor of the activated dissipative conductivity in a plateau range of the quantum Hall effect is studied in the case of a long-range random potential. It is shown that due to long time it takes for an electron to drift along the perimeter of a large percolation cluster, phonons are able to maintain quasi-equilibrium inside the cluster. The saddle points separating such clusters may then be viewed as ballistic point contacts between electron reservoirs with different electrochemical potentials. The prefactor is universal and equal to 2$e^2/h$ at an integer filling factor $\nu$ and to 2$e^2/q^{2}h$ at $\nu=p/q$.Comment: 4 pages + 2 figures by reques