Biomedical subjects
Publications and source records attributed to P Reimann.
Thermally activated escape over a potential barrier in the presence of periodic driving is considered. By means of novel time-dependent path-integral methods we derive asymptotically exact weak-noise expressions for both the instantaneous and the time-averaged escape rate. The agreement with accurate numerical results is excellent over a wide range of driving strengths and driving frequencies.
We consider a silicon wafer, pierced by millions of identical pores with periodically varying diameters but without spatial inversion symmetry (ratchet profile). When a liquid is periodically pumped back and forth through the pores, our theory predicts a net transport of suspended micrometer-sized particles (drift ratchet). The direction of this particle current depends very sensitively on the size of the particles. For typical parameter values of the experiment, two different types of particles at an initially homogeneous 1:1 mixture are spatially separated with a purity beyond 1:1000 on a time scale of a few hours in comparably large quantities. This result is due to the highly parallel architecture of the device. The experimental realization of the setup, presently under construction, thus appears to be a promising new particle separation device, possibly superior to existing methods for particles sizes on the micrometer scale.
We consider the Brownian motion of a quantum-mechanical particle in a one-dimensional parabolic potential with periodically modulated curvature under the influence of a thermal heat bath. Analytic expressions for the time-dependent position and momentum variances are compared with results of an iterative algorithm, the so-called quasiadiabatic propagator path-integral algorithm. We obtain good agreement over an extended range of parameters for this spatially continuous quantum system. These findings indicate the reliability of the algorithm also in cases for which analytic results may not be available a priori.
We consider the thermally activated escape of an overdamped Brownian particle over a potential barrier in the presence of periodic driving. A time-dependent path-integral formalism is developed which allows us to derive asymptotically exact weak-noise expressions for both the instantaneous and the time-averaged escape rate. Our results comprise a conceptually different, systematic treatment of the rate prefactor multiplying the exponentially leading Arrhenius factor. Moreover, an estimate for the deviations at finite noise strengths is provided and a supersymmetry-type property of the time-averaged escape rate is verified. For piecewise parabolic potentials, the rate expression can be evaluated in closed analytical form, while in more general cases, as exemplified by a cubic potential, an action-integral remains to be minimized numerically. Our comparison with very accurate numerical results demonstrates an excellent agreement with the theoretical predictions over a wide range of driving strengths and driving frequencies.
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Between 1967 and 1982, intraaortic balloon pumping (IABP) was attempted in 733 patients. Of these, 132 were diabetic: 51 patients were managed with diet alone, 46 patients took oral hypoglycemic agents and 35 patients required insulin. Vascular complications associated with IABP occurred in 34% of the insulin-dependent diabetics, in 18% of other diabetics and in 14% of nondiabetic patients. Infectious complications were 37, 22 and 25%, respectively. Seventy-five diabetic patients (57%) were discharged alive from the hospital after balloon pumping, essentially the same proportion as among nondiabetic patients (58%). It is concluded that although diabetics incur a higher complication rate, IABP is not contraindicated.
To compare the percutaneous and surgical techniques of intraaortic balloon pump insertion, 101 patients referred for this procedure were randomly assigned to either percutaneous or surgical insertion. Insertion using the designated technique was successful in 45 (88%) of 51 patients with percutaneous insertion and 48 (96%) of 50 patients with surgical insertion (difference not statistically significant). The time from the beginning of the insertion procedure to the initiation of counterpulsation was 13 +/- 8 minutes for the percutaneous technique versus 31 +/- 16 minutes for the surgical technique (p less than 0.001). In the percutaneous group, 10 patients required Fogarty thrombectomy after balloon pump removal, and 1 patient developed severe leg ischemia requiring immediate termination of balloon pump support. In the surgical group, one patient developed leg ischemia requiring surgical intervention, three patients developed sepsis with bacteremia (including one patient who required vein patch repair of the femoral artery), one patient developed a wound infection requiring debridement and one patient had a cerebral embolus. Aortic dissection, aortoiliac perforation or amputation did not occur in either group. Major vascular complications occurred in 11 patients (22%) with percutaneous insertion versus 2 patients (4%) with surgical insertion (p less than 0.05). It is concluded that although the percutaneous technique for intraaortic balloon pump insertion is faster than the surgical technique and is technically easy, it is associated with a higher incidence of vascular complications.
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