434 research outputs found
Cancellation of Glauber gluon exchange in the double Drell-Yan process
An essential part of any factorisation proof is the demonstration that the
exchange of Glauber gluons cancels for the considered observable. We show this
cancellation at all orders for double Drell-Yan production (the double parton
scattering process in which a pair of electroweak gauge bosons is produced)
both for the integrated cross section and for the cross section differential in
the transverse boson momenta. In the process of constructing this proof, we
also revisit and clarify some issues regarding the Glauber cancellation
argument and its relation to the rest of the factorisation proof for the single
Drell-Yan process.Comment: 65 pages, 23 figure
Multisensor Data Fusion Implementation for a Sensor Based Fertilizer Application System
"Mapping systems" (“mapping approach”), real-time sensor-actuator systems ("sensor
approach") or the combination of both (“Real-time approach with map overlay”) determine the
process control in mobile application systems for spatially variable fertilization. Within the
integrated research project “Information Systems Precision Farming Duernast” (IKB Duernast)
the implementation of the “Real-time approach with map overlay” was done for intensive
nitrogen fertilization. The bottom line of this sophisticated approach is a comprehensive situation
assessment, a typical multisensor data fusion task. Based on a functional and procedural
modelling of the multisensor data fusion and decision making process, it could be pointed out
that an expert system is an adequate fusion paradigm and algorithm. Therefore, a software
simulation with an expert system as core element was implemented to fuse on-line sensor
technology measurements (REIP), maps (yield, EM38, environmental constraints, draft force)
and user inputs in order to derive an application set point in real-time. The development of an
expert system can be viewed as a structured transformation in five levels from the “specification
level”, the “task level”, the “problem solving level” and the “knowledge base level” to the “tool
level”. In the “tool level” the hybrid expert system shell JESS (Java Expert System Shell) was
selected for implementation due to the results of preceding levels. Knowledge acquisition was
done within another IKB-subproject by the means of data mining. Typical and maximal times of
10 ms and 60 ms for one fusion cycle were measured running this application on a 32-bit
processor hardware (Intel Pentium III Mobile, 1 GHz)
Circular Permutation in the Ω-Loop of TEM-1 β-Lactamase Results in Improved Activity and Altered Substrate Specificity
Generating diverse protein libraries that contain improved variants at a sufficiently high frequency is critical for improving the properties of proteins using directed evolution. Many studies have illustrated how random mutagenesis, cassette mutagenesis, DNA shuffling and similar approaches are effective diversity generating methods for directed evolution. Very few studies have explored random circular permutation, the intramolecular relocation of the N- and C-termini of a protein, as a diversity-generating step for directed evolution. We subjected a library of random circular permutations of TEM-1 β-lactamase to selections on increasing concentrations of a variety of β-lactam antibiotics including cefotaxime. We identified two circularly permuted variants that conferred elevated resistance to cefotaxime but decreased resistance to other antibiotics. These variants were circularly permuted in the Ω-loop proximal to the active site. Remarkably, one variant was circularly permuted such that the key catalytic residue Glu166 was located at the N-terminus of the mature protein
Phase diagram of turbulence in superfluid 3He-B
In superfluid 3He-B mutual-friction damping of vortex-line motion decreases
roughly exponentially with temperature. We record as a function of temperature
and pressure the transition from regular vortex motion at high temperatures to
turbulence at low temperatures. The measurements are performed with
non-invasive NMR techniques, by injecting vortex loops into a long column in
vortex-free rotation. The results display the phase diagram of turbulence at
high flow velocities where the transition from regular to turbulent dynamics is
velocity independent. At the three measured pressures 10.2, 29.0, and 34 bar,
the transition is centered at 0.52--0.59Tc and has a narrow width of 0.06Tc
while at zero pressure turbulence is not observed above 0.45Tc.Comment: To be published in J. Low Temp. Phys. (QFS2004 proceedings
Deciphering the folding kinetics of transmembrane helical proteins
Nearly a quarter of genomic sequences and almost half of all receptors that
are likely to be targets for drug design are integral membrane proteins.
Understanding the detailed mechanisms of the folding of membrane proteins is a
largely unsolved, key problem in structural biology. Here, we introduce a
general model and use computer simulations to study the equilibrium properties
and the folding kinetics of a -based two helix bundle fragment
(comprised of 66 amino-acids) of Bacteriorhodopsin. Various intermediates are
identified and their free energy are calculated toghether with the free energy
barrier between them. In 40% of folding trajectories, the folding rate is
considerably increased by the presence of non-obligatory intermediates acting
as traps. In all cases, a substantial portion of the helices is rapidly formed.
This initial stage is followed by a long period of consolidation of the helices
accompanied by their correct packing within the membrane. Our results provide
the framework for understanding the variety of folding pathways of helical
transmembrane proteins
Transition to superfluid turbulence governed by an intrinsic parameter
Hydrodynamic flow in both classical and quantum fluids can be either laminar
or turbulent. To describe the latter, vortices in turbulent flow are modelled
with stable vortex filaments. While this is an idealization in classical
fluids, vortices are real topologically stable quantized objects in
superfluids. Thus superfluid turbulence is thought to hold the key to new
understanding on turbulence in general. The fermion superfluid 3He offers
further possibilities owing to a large variation in its hydrodynamic
characteristics over the experimentally accessible temperatures. While studying
the hydrodynamics of the B phase of superfluid 3He, we discovered a sharp
transition at 0.60Tc between two regimes, with regular behaviour at
high-temperatures and turbulence at low-temperatures. Unlike in classical
fluids, this transition is insensitive to velocity and occurs at a temperature
where the dissipative vortex damping drops below a critical limit. This
discovery resolves the conflict between existing high- and low-temperature
measurements in 3He-B: At high temperatures in rotating flow a vortex loop
injected into superflow has been observed to expand monotonically to a single
rectilinear vortex line, while at very low temperatures a tangled network of
quantized vortex lines can be generated in a quiescent bath with a vibrating
wire. The solution of this conflict reveals a new intrinsic criterion for the
existence of superfluid turbulence.Comment: Revtex file; 5 pages, 2 figure
Dynamic in vitro measurement of patellar movement after total knee arthroplasty: an in vitro study
BACKGROUND: Changing the kinematic behaviour of patellar movement could be one of the reasons for anterior knee pain after implantation of a total knee arthroplasty (TKA). The aim of the current study was to measure the potential influence on patellar kinematics of patellar resurfacing during TKA. METHODS: Patellar movement before and after TKA with and without patellar resurfacing was measured under dynamic conditions in an in vitro cadaver simulation. Physiologic Musculus quadriceps forces were applied to five physiologic human knee specimens undergoing simulated isokinetic extension motions, patellar movement was measured using an ultrasonic measurement system. Thereafter, the Interax(® )I.S.A.-prosthesis system was implanted without and with resurfacing the patella, and patellar movement was again measured. RESULTS: The physiologic patella center moved on a semilunar path up to 6.4 mm (SD 6.4 mm) medially during extension. After TKA, the unresurfaced patella showed significantly less medial translation (p = 0.04) than the resurfaced patella. Subsequent resurfacing of the patella then resulted in a return to mediolateral positioning of the patella similar to the physiological case, whereas the resurfaced patella tilted up to twice as much as physiologic. CONCLUSION: The results of this study suggest that resurfacing of the patella during TKA can result in a restoration of the physiologic mediolateral shift of the patellofemoral joint while angulation of the patella remains unphysiologic
Rotating Superfluid Turbulence
Almost all studies of vortex states in helium II have been concerned with
either ordered vortex lattices or disordered vortex tangles. This work studies
numerically what happens in the presence of both rotation (which induces order)
and thermal counterflow (which induces disorder). We find a new statistically
steady state in which the vortex tangle is polarized along the rotational axis.
Our results are used to interpret an instability which was discovered
experimentally by Swanson et al. years ago but has been unexplained until now
Non-Anatomic Proximal Realignment for Recurrent Patellar Dislocation Does Not Sufficiently Prevent Redislocation
Several operative techniques have been described for recurrent patellar dislocation. Clinical results vary depending on the procedure and indication. The present study aimed to evaluate the clinical outcome of Insall’s proximal realignment for recurrent patellar dislocation at mid-term follow-up. Forty-five patients were reviewed with a mean follow-up period of 49 months after having undergone Insall’s procedure. Outcome measures included reports of redislocations, complications, patient-reported outcome scores (Kujala, Tegner activity scale) and subjective assessment. No statistically significant improvements (p < 0.05) in patient-reported outcome measures were noted. Sixteen patients (35%) had poor to fair results using the Kujala score. Subjective assessment revealed that 12 patients (27%) were dissatisfied with the outcome of their surgery and would not undergo the same procedure. Ten patients (22%) had suffered from redislocation at the latest follow-up. In 4 cases (9%), intra-articular knee hematoma occurred which required arthroscopic intervention. The overall mid-term outcome of the present study shows low patient satisfaction. Non-anatomic realignment for recurrent patellar dislocation does not adequately prevent redislocation
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