Small Stop Research Articles

High resolution 3D NanoImprint technology: Template fabrication, application in Fabry–Pérot-filter-array-based optical nanospectrometers

We report a novel 3D NanoImprint methodology with very high vertical resolution well below 1nm and a minimum surface roughness down to 0.2nm in root mean square (rms) which is attractive for several applications. We introduce our 3D NanoImprint methodology in fabricating 3D filter cavities of Fabry-Perot filter arrays for optical nanospectrometers. A large number of different cavity heights can be fabricated in one single imprint step using this high resolution, low-cost 3D NanoImprint technology. The key issue of developing 3D NanoImprint technology is the fabrication of high resolution templates. The novel 3D templates contain arrays of negative or positive checkerboard-like mesa structures with currently up to 64 different heights. Different types of 3D templates were developed and adapted to cutting edge NanoImprint methods and imprint resists. The performance of different 3D NanoImprint recipes was investigated. Based on the novel 3D NanoImprint technology developed in this work, static Fabry-Perot filter arrays with NanoImprinted cavities indicated rather high filter transmission (best single filter >90%), small line widths (about 2nm in full width at half maximum) and broad stop bands.

Turbulence-induced collision velocities and rates between different sized dust grains

We study the collision rates and velocities for point-particles of different sizes in turbulent flows. We construct fits for the collision rates at specified velocities (effectively a collisional velocity probability distribution) for particle stopping time ratios up to four; already by that point the collisional partners are very poorly correlated and so the results should be robust for even larger stopping time ratios. Significantly, we find that while particles of very different masses have approximately Maxwellian collisional statistics, as the mass ratio shrinks the distribution changes dramatically. At small stopping time ratios, the collisional partners are highly correlated and we find a population of high number density (clustered), low relative-velocity particle pairs. Unlike in the case of identical stopping time collisional partners, this low relative-velocity clustered population is collisional, but the clustering is barely adequate to trigger bulk effects such as the streaming instability. We conclude our analysis by constructing a master fit to the collisional statistics as a function only of the stopping time ratio. Together with our previous work for identical stopping time particle pairs, this provides a recipe for including collisional velocity probability distributions in dust coagulation models for protoplanetary disks. We also include our recipe for determining particle collisional diagnostics from numerical simulations.

Precision unification in λSUSY with a 125GeV Higgs

It is challenging to explain the tentative 125 GeV Higgs signal in the Minimal Supersymmetric Standard Model (MSSM) without introducing excessive fine-tuning, and this motivates the study of non-minimal implementations of low energy supersymmetry (SUSY). A term \lambda SH_uH_d involving a Standard Model (SM) singlet state S leads to an additional source for the quartic interaction raising the mass of the lightest SM-like Higgs. However, in order to achieve m_h \approx 125 GeV with light stops and small stop mixing, it is necessary for \lambda \gtrsim 0.7 and consequently \lambda may become non-perturbative before the unification scale. Moreover, as argued by Barbieri, Hall, et al. low fine-tuning prefers the region \lambda~1-2, leading to new or non-perturbative physics involving S below the GUT scale (`\lambda SUSY' models). This raises the concern that precision gauge coupling unification, the prime piece of indirect experimental evidence for low energy SUSY, may be upset. Using the NSVZ exact \beta-function along with well motivated assumptions on the strong coupling dynamics we show that this is not necessarily the case, but rather there exist classes of UV completions where the strong-coupling effects can naturally correct for the present ~3% discrepancy in the two-loop MSSM unification prediction for \alpha_s. Moreover, we argue that in certain scenarios a period of strong coupling can also be beneficial for t-b unification, while maintaining the small to moderate values of tan\beta preferred by the Higgs mass.

Dusty gas with smoothed particle hydrodynamics - I. Algorithm and test suite

We present a new algorithm for simulating two-fluid gas and dust mixtures in Smoothed Particle Hydrodynamics (SPH), systematically addressing a number of key issues including the generalised SPH density estimate in multi-fluid systems, the consistent treatment of variable smoothing length terms, finite particle size, time step stability, thermal coupling terms and the choice of kernel and smoothing length used in the drag operator. We find that using double-hump shaped kernels improves the accuracy of the drag interpolation by a factor of several hundred compared to the use of standard SPH bell-shaped kernels, at no additional computational expense. In order to benchmark our algorithm, we have developed a comprehensive suite of standardised, simple test problems for gas and dust mixtures: dustybox, dustywave, dustyshock, dustysedov and dustydisc, the first three of which have known analytic solutions. We present the validation of our algorithm against all of these tests. In doing so, we show that the spatial resolution criterion \Delta < cs ts is a necessary condition in all gas+dust codes that becomes critical at high drag (i.e. small stopping time ts) in order to correctly predict the dynamics. Implicit timestepping and the implementation of realistic astrophysical drag regimes are addressed in a companion paper.

Predicted photonic band gaps in diamond-lattice crystals built from silicon truncated tetrahedrons

Recently, a silicon micromachining method to produce tetrahedral silicon particles was discovered. In this report we determine, using band structure calculations, the optical properties of diamond-lattice photonic crystals when assembled from such particles. We show that crystal structures built from silicon tetrahedra are expected to display small stop gaps. Wide photonic band gaps appear when truncated tetrahedral particles are used to build the photonic crystals. With truncated tetrahedral particles, a bandgap with a width of 23.6% can be achieved, which is more than twice as wide compared to band gaps in self-assembled diamond-lattices of hard-spheres. The width of the bandgap is insensitive to small deviations from the optimal amount of truncation. This work paves the way to a novel class of silicon diamond-lattice bandgap crystals that can be obtained through self-assembly. Such a self-assembly approach would allow for easy integration of these highly photonic crystals in existing silicon microfluidic and -electronic systems.

Increasing the alkaline protease activity of Bacillus cereus and Bacillus polymyxa simultaneously with the start of sporulation phase as a defense mechanism

In this research, the growth curve, curve of sporulation phase and alkaline protease activity of Bacillus cereus and Bacillus polymyxa were compared and examined simultaneously. These examinations showed that, the production of alkaline protease started with the beginning of the log phase in the growth curve simultaneously and after a small stop according to the stationary phase increased and then with the start of the death phase, increased rapidly again. The maximum alkaline protease activities of B. polymyxa and B. cereus were measured at the death phase of the growth curve and at the start of the sporulation phase of the two microorganisms. The mentioned experiments were made in glucose synthetic medium at 30°C with 100 rpm aeration speed for 144 h. The maximum alkaline protease activity of B. cereus and B. polymyxa occurred after 72 h simultaneously with the start of the sporulation phase of the two bacteria and were measured at 383 and 418 u/ml, respectively. The next experiments showed that, the enzyme was very stable in extreme conditions such as freezing, drying and lyophilization. Also, it protected 98 to 100% of its primary activity after 4 months in the mentioned conditions. Key words: Sporulation phase, alkaline protease, Bacillus cereus, Bacillus polymyxa, extreme conditions.

Design of good QC-LDPC codes without small girth in the p-plane

A construction method based on the p-plane to design high-girth quasi-cyclic low-density parity-check (QC-LDPC) codes is proposed. Firstly the good points in every line of the p-plane can be ascertained through filtering the bad points, because the designed parity-check matrixes using these points have the short cycles in Tanner graph of codes. Then one of the best points from the residual good points of every line in the p-plane will be found, respectively. The optimal point is also singled out according to the bit error rate (BER) performance of the QC-LDPC codes at last. Explicit necessary and sufficient conditions for the QC-LDPC codes to have no short cycles are presented which are in favor of removing the bad points in the p-plane. Since preventing the short cycles also prevents the small stopping sets, the proposed construction method also leads to QC-LDPC codes with a higher stopping distance.

Preliminary application study of Ligasure in video-assisted thoracic pulmonary surgery

To investigate the application and techniques of Ligasure in video-assisted thoracic pulmonary surgery. Use Ligasure to dissect lung parenchyma, small pulmonary vessel and stop bleeding in 15 cases spontaneous pneumothorax and 20 cases peripheral single lung node who undertaken video-assisted thoracic surgery during October 2008 to June 2010. All the procedures were successful, no severe complications, as active bleeding, continuous air leak occurred. A period of 9.3 months (2 - 18 months) follow-up of all patients shows no delayed bleeding or recurrence pneumothorax. Ligasure is safe, easy to use. It can optimize operation and reduce the operation time.

Ruling out small stopping sets and small girth in Tanner graph of QC-LDPC code

Ruling out small stopping sets and small girth in Tanner graph of QC-LDPC code

On asymptotic ensemble weight enumerators of LDPC-like codes

For LDPC-like codes such as LDPC, GLDPC, and DGLDPC codes, it is well known that the error floor can be caused by the codewords of small weights or stopping sets of small sizes. In this paper, we investigate the computation of asymptotic weight enumerators such that it becomes a convenient tool to determine a good distribution of code ensembles. In addition, by analyzing the first order approximation, we derive a condition to obtain a negative asymptotic growth rate of the codewords of small linear-sized weights, which is an important constraint for distribution optimization. Also the weight enumerators of turbo and repeat-accumulate codes are investigated. Furthermore, we extend our results to nonbinary DGLDPC codes. Generalization to N-layer and convolutional code based LDPC-like codes are also developed.

Eliminating small stopping sets in irregular low-density parity-check codes

We present a novel scheme to eliminate small stopping sets in irregular low-density parity-check (LDPC) codes. By adding several new check nodes and having their edges connected to small stopping sets in the original code, the improved code decreases the number of small stopping sets efficiently. Simulation results show that the proposed scheme decreases the frame error rate (FER) significantly in the error floor region, whereas having almost the same rate as the original code.

Probe prototypes based on TlBr detectors

Abstract Detectors based on TlBr crystals are ideally suited for the probes, where small size and rapid stopping power are highly desirable attributes. The development results of TlBr probes for medical and nuclear industry applications are presented here. Probes for both applications include TlBr detectors with dimensions of 5×5×2 mm 3 and a microelectronics preamplifier. The different construction and technological aspects of probes designed for both application types are discussed. The probes were tested over a wide energy range. We obtained energy resolutions of 3.6, 4.9 and 14.5 keV at energies of 59.6, 122 and 662 keV, respectively, for the developed probe prototypes at room temperature. The observed performances of probe prototypes having TlBr detectors confirmed their promising potential for probe applications.

Small stopping sets in Steiner triple systems

The size of the smallest stopping set in a low-density parity check (LDPC) code determines, to an extent, the performance of iterative decoding methods over the binary erasure channel. In an LDPC code arising from a block design, a stopping set is a subset of its blocks with the property that every point belonging to one of the selected blocks belongs to at least two of them. While some Steiner triple systems have no stopping sets of size 5 or less, it is shown that every Steiner triple system has a stopping set of size at most 7. The proof can be viewed as an application of polynomial identities among configuration counts that generalize the family of known linear identities. While no example of a Steiner triple system whose smallest stopping set has size seven is known, it is shown that a partial Steiner triple system on v points with c·v 1.8 triples that has no stopping set of size less than 7 exists.

Turbo Codes in Binary Erasure Channel

In this correspondence, the stopping set of turbo codes with iterative decoding in the binary erasure channel is defined. Block and bit erasure probabilities of turbo codes are studied by using the stopping set analysis. It is found that block and bit erasure probabilities of turbo codes with iterative decoding are higher than those with maximum-likelihood decoding, where the differences are negligible in the error floor region. It is shown that in the error floor region, block and bit erasure probabilities of turbo codes with iterative decoding are dominated by small stopping sets and are asymptotically dominated by low weight codewords.

Clinical trial design in status epilepticus: problems and solutions

This paper is written from a pediatric perspective. The starting point in trial design is the identification of important questions, particularly those about therapeutic purposes. The main justification for clinical trials is that status epilepticus is harmful and therefore needs to be treated. In terms of permanent CNS damage and epilepsy following status epilepticus, the rates in published studies vary between 4% and 40% depending on their quality (Raspall-Chaure et al., 2006) and none have looked for subtle cognitive impairments which might be suggested by the finding of acute hippocampal edema following febrile convulsive status epilepticus (CSE) (Scott et al., 2002, 2003). Thus, we are left with a general view that it would be better if we could safely reduce the time that children are convulsing. However, the expense and effort of a randomized controlled trial (RCT) needs to be justified as alternative approaches for example, well-designed epidemiological studies may also provide useful therapeutic information for achieving this goal. The types of questions requiring clinical trial fall into two groups: drug related and clinical approach related.

LDPC Code Construction with Low Error Floor Based on the IPEG Algorithm

We propose a modification on the improved progressive-edge-growth(IPEG) algorithm. Proposed modification increases the connectivity of variable nodes using extrinsic message degree of variable nodes, which results in reducing the small stopping sets. Through computer simulation, we confirm that the codes constructed by the proposed algorithm have lower error floor than those constructed by the original IPEG algorithm.

Mechanism for cavitation of monoleaflet and bileaflet valves in an artificial heart

It is possible that mechanical heart valves mounted in an artificial heart close much faster than those used for clinical valve replacement, resulting in the formation of cavitation bubbles. In this study, the mechanism for mechanical heart cavitation was investigated using the Medtronic Hall monoleaflet valve and the Sorin Bicarbon bileaflet valve mounted at the mitral position in an electrohydraulic total artificial heart. The valve-closing velocity was measured with a charge-coupled device (CCD) laser displacement sensor, and images of mechanical heart valve cavitation were recorded using a high-speed video camera. The valve-closing velocity of the Sorin Bicarbon bileaflet valve was lower than that of the Medtronic Hall monoleaflet valve. Most of the cavitation bubbles generated by the monoleaflet valve were observed near the valve stop; with the Sorin Bicarbon bileaflet valve, cavitation bubbles were concentrated along the leaflet tip. The cavitation density increased as the valve-closing velocity and the valve stop area increased. These results strongly indicate that squeeze flow holds the key to cavitation in the mechanical heart valve. From the perspective of squeeze flow, bileaflet valves with a low valve-closing velocity and a small valve stop area may cause less blood cell damage than monoleaflet valves.

Mechanism for cavitation of monoleaflet and bileaflet valves in an artificial heart

It is possible that mechanical heart valves mounted in an artificial heart close much faster than those used for clinical valve replacement, resulting in the formation of cavitation bubbles. In this study, the mechanism for mechanical heart cavitation was investigated using the Medtronic Hall monoleaflet valve and the Sorin Bicarbon bileaflet valve mounted at the mitral position in an electrohydraulic total artificial heart. The valve-closing velocity was measured with a charge-coupled device (CCD) laser displacement sensor, and images of mechanical heart valve cavitation were recorded using a high-speed video camera. The valve-closing velocity of the Sorin Bicarbon bileaflet valve was lower than that of the Medtronic Hall monoleaflet valve. Most of the cavitation bubbles generated by the monoleaflet valve were observed near the valve stop; with the Sorin Bicarbon bileaflet valve, cavitation bubbles were concentrated along the leaflet tip. The cavitation density increased as the valve-closing velocity and the valve stop area increased. These results strongly indicate that squeeze flow holds the key to cavitation in the mechanical heart valve. From the perspective of squeeze flow, bileaflet valves with a low valve-closing velocity and a small valve stop area may cause less blood cell damage than monoleaflet valves.

Mechanism for cavitation phenomenon in mechanical heart valves

Recently, cavitation on the surface of mechanical heart valve has been studied as a cause of fractures occurring in implanted Mechanical Heart Valves (MHVs). It has been conceived that the MHVs mounted in an artificial heart close much faster than in vivo sue, resulting in cavitation bubbles formation. In this study, six different kinds of monoleaflet and bileaflet valves were mounted in the mitral position in an Electro-Hydraulic Total Artificial Heart (EHTAH), and we investigated the mechanisms for MHV cavitation. The valve closing velocity and a high speed video camera were employed to investigate the mechanism for MHV cavitation. The closing velocity of the bileaflet valves was slower than that of the monoleaflet valves. Cavitation bubbles were concentrated on the edge of the valve stop and along the leaflet tip. It was established that squeeze flow holds the key to MHV cavitation in our study. Cavitation intensity increased with an increase in the valve closing velocity and the valve stop area. With regard to squeeze flow, the bileaflet valve with slow valve-closing velocity and small valve stop areas is better able to prevent blood cell damage than the monoleaflet valves.

Operational specifications of the laser illuminated track etch scattering dosemeter reader

The personnel dosimetry operations team at the Los Alamos National Laboratory (LANL) has accepted the laser illuminated track etch scattering (LITES) dosemeter reader into its suite of radiation dose measurement instruments. The LITES instrument transmits coherent light from a He-Ne laser through the pertinent track etch foil and a photodiode measures the amount of light scattered by the etched tracks. A small beam stop blocks the main laser light, while a lens refocuses the scattered light into the photodiode. Three stepper motors in the current LITES system are used to position a carousel that holds 36 track etch dosemeters (TEDs). Preliminary work with the LITES system demonstrated the device had a linear response in counting foils subjected to exposures up to 50 mSv (5.0 rem). The United States Department of Energy requires that the annual general employee dose not exceed 50 mSv (5.0 rem). On a regular basis, LANL uses the Autoscan-60 reader system (Thermo Electron Corp.) for counting track etch dosemeters. However, LANL uses a 15 h etch process for CR-39 dosemeters, and this produces more and larger track etch pits than the 6 h etch used by many institutions. Therefore, LANL only uses the Autoscan-60 for measuring neutron dose equivalent up to exposure levels of approximately 3 mSv (300 mrem). The LITES system has a measured lower limit of detection of approximately 0.6 mSv (60 mrem), and it has a correlation coefficient of R (2) = 0.99 over an exposure range up to 500 mSv (50.0 rem). A series of blind studies were done using three methods: the Autoscan-60 system, manual counting by optical microscope and the LITES instrument. A collection of track etch dosemeters of unknown neutron dose equivalent (NDE) were analysed using the three methods, and the performance coefficient (PC) was calculated when the NDE became known. The Autoscan-60 and optical microscope methods had a combined PC = 0.171, and the LITES instrument had a PC = 0.194, where a PC less than or equal to 0.300 is considered satisfactory.