Measurements of the Young’s modulus of hydroxide catalysis bonds, and the effect on thermal noise in ground-based gravitational wave detectors

With the outstanding results from the detection and observation of gravitational waves from coalescing black holes and neutron star inspirals, it is essential that pathways to further improve the sensitivities of the LIGO and VIRGO detectors are explored. There are a number of factors that potentially limit the sensitivities of the detectors. One such factor is thermal noise, a component of which results from the mechanical loss in the bond material between the silica fibre suspensions and the test mass mirrors. To calculate its magnitude, the Young’s modulus of the bond material has to be known with reasonable accuracy. In this paper we present a new combination of ultrasonic technology and Bayesian analysis to measure the Young’s modulus of hydroxide catalysis bonds between fused silica substrates. Using this novel technique, we measure the bond Young’s modulus to be 18.5 ± 2.0 2.3     GPa . We show that by applying this value to thermal noise models of bonded test masses with suitable attachment geometries, a reduction in suspension thermal noise consistent with an overall design sensitivity improvement allows a factor of 5 increase in event rate to be achieved

Certified Roundoff Error Bounds Using Semidefinite Programming.

Roundoff errors cannot be avoided when implementing numerical programs with finite precision. The ability to reason about rounding is especially important if one wants to explore a range of potential representations, for instance for FPGAs or custom hardware implementation. This problem becomes challenging when the program does not employ solely linear operations as non-linearities are inherent to many interesting computational problems in real-world applications. Existing solutions to reasoning are limited in the presence of nonlinear correlations between variables, leading to either imprecise bounds or high analysis time. Furthermore, while it is easy to implement a straightforward method such as interval arithmetic, sophisticated techniques are less straightforward to implement in a formal setting. Thus there is a need for methods which output certificates that can be formally validated inside a proof assistant. We present a framework to provide upper bounds on absolute roundoff errors. This framework is based on optimization techniques employing semidefinite programming and sums of squares certificates, which can be formally checked inside the Coq theorem prover. Our tool covers a wide range of nonlinear programs, including polynomials and transcendental operations as well as conditional statements. We illustrate the efficiency and precision of this tool on non-trivial programs coming from biology, optimization and space control. Our tool produces more precise error bounds for 37 percent of all programs and yields better performance in 73 percent of all programs

Revisiting the Jurassic Geomagnetic Reversal recorded in the Lesotho Basalt (Southern Africa)

We carried out a detailed and continuous paleomagnetic sampling of the reversed to normal geomagnetic transition recorded by some 60 consecutive flow units near the base of the Lesotho Basalt (183  1 Ma). After alternating field or thermal cleaning the directions of remanence are generally well clustered within flow units. In contrast, the thermal instability of the samples did not allow to obtain reliable paleointensity determinations. The geomagnetic transition is incompletely recorded due to a gap in volcanic activity attested both by eolian deposits and a large angular distance between the field directions of the flows underlying or overlying these deposits. The transition path is noticeably different from that reported in the pioneer work of van Zijl et al. (1962). The most transitional Virtual Geomagnetic Poles are observed after the volcanic hiatus. Once continents are replaced in their relative position 180 Ma ago, the post-hiatus VGP cluster over Russia. However, two successive rebounds from that cluster are found, with VGP reaching repeatedly Eastern Asia coast. Thus, the VGP path is not narrowly constrained in paleolongitude. The decrease in intensity of magnetization as the field deviates from the normal or reversed direction suggests that the decrease in field magnitude during the reversal reached 80-90%. We conclude that although the reversal is of a dipole of much weaker moment than that which existed on average during Cenozoic time, the characteristics of the reversing geodynamo seem to be basically similar.Comment: Paper No GD124 submitted to Geophysical Journal International. Received in original form 20/01/2003, accepted 09/04/200

MEGAHIT: An ultra-fast single-node solution for large and complex metagenomics assembly via succinct de Bruijn graph

MEGAHIT is a NGS de novo assembler for assembling large and complex metagenomics data in a time- and cost-efficient manner. It finished assembling a soil metagenomics dataset with 252Gbps in 44.1 hours and 99.6 hours on a single computing node with and without a GPU, respectively. MEGAHIT assembles the data as a whole, i.e., it avoids pre-processing like partitioning and normalization, which might compromise on result integrity. MEGAHIT generates 3 times larger assembly, with longer contig N50 and average contig length than the previous assembly. 55.8% of the reads were aligned to the assembly, which is 4 times higher than the previous. The source code of MEGAHIT is freely available at https://github.com/voutcn/megahit under GPLv3 license.Comment: 2 pages, 2 tables, 1 figure, submitted to Oxford Bioinformatics as an Application Not

Search for Magnetic Monopoles Trapped in Matter

There have been many searches for magnetic monopoles in flight, but few for monopoles in matter. We have searched for magnetic monopoles in meteorites, schists, ferromanganese nodules, iron ores and other materials. The detector was a superconducting induction coil connected to a SQUID (Superconducting Quantum Interference Device) with a room temperature bore 15 cm in diameter. We tested a total of more than 331 kg of material including 112 kg of meteorites. We found no monopole and conclude the overall monopole/nucleon ratio in the samples is $<1.2 \times 10^{-29}$ with a 90\% confidence level.Comment: 6 pages, rev tex, no figure

Investigation of the composition of the Luna 16 lunar sample

The concentrations of aluminum, manganese, sodium, chromium, iron, cobalt, and 12 rare earth elements were determined by neutron activation analysis using slow neutrons. Oxygen and silicon were determined using a fast neutron generator. Mossbauer spectroscopy was used to investigate iron compounds in Luna 16 regolith samples from the upper part of the core

An effective all-atom potential for proteins

We describe and test an implicit solvent all-atom potential for simulations of protein folding and aggregation. The potential is developed through studies of structural and thermodynamic properties of 17 peptides with diverse secondary structure. Results obtained using the final form of the potential are presented for all these peptides. The same model, with unchanged parameters, is furthermore applied to a heterodimeric coiled-coil system, a mixed alpha/beta protein and a three-helix-bundle protein, with very good results. The computational efficiency of the potential makes it possible to investigate the free-energy landscape of these 49--67-residue systems with high statistical accuracy, using only modest computational resources by today's standards

Engineered turns of a recombinant antibody improve its in vivo folding

Using recombinant antibodies functionally expressed by secretion to the periplasm in Escherichia coli as a model system, we identified mutations located in turns of the protein which reduce the formation of aggregates during in vivo folding or which influence cell stability during expression. Unexpectedly, the two effects are based on different mutations and could be separated, but both mutations act synergistically in vivo. Neither mutation increases the thermodynamic stability in vitro. However, the in vivo folding mutation correlates with the yield of oxidative folding in vitro, which is limited by the side reaction of aggregation. The in vivo folding data also correlate with the rate and activation entropy of thermally induced aggregation. This analysis shows that it is possible to engineer improved frameworks for semi-synthetic antibody libraries which may be important in maintaining library diversity. Moreover, limitations in recombinant protein expression can be overcome by single amino acid substitution