Search results for "Topping"
showing 10 items of 56 documents
Stopping powers of havar and effective charge for 1.4–3.2 MeV/u 127I-ions
2000
Abstract Stopping powers of havar for 1.4–3.2 MeV/u 127 I-ions have been determined by the transmission technique using two geometrical arrangements. No previous data have been published for havar with this ion. The experimental data are compared with predictions obtained by using Bragg’s additivity rule with various parametrizations of the stopping power found in the literature. The values obtained by the parametrizations underestimate the experimental data by 5–11%. The empirical correction scheme of Thwaites yields values in rather good agreement with the present results, especially at energies above 1.9 MeV/u. The effective charges of the 127 I ions were also deduced from the experiment…
Early virologic response with pegylated interferons
2004
Abstract Recently, 12-week evaluation of viral response has been recommended as a means of reducing antiviral treatment morbidity and costs. The development of early stopping rules relies on an important assumption: rules must minimise discontinuation of treatment in patients who might ultimately respond after completion of the full course of therapy. Minimising loss of potential responders is the most important clinical goal in defining an early stopping rule because it provides the most sustained virological responders. This definition of the rule relies on maximising the negative predictive value. Conversely, rules that select patients based on optimising the positive predictive value pr…
On an approximation problem for stochastic integrals where random time nets do not help
2006
Abstract Given a geometric Brownian motion S = ( S t ) t ∈ [ 0 , T ] and a Borel measurable function g : ( 0 , ∞ ) → R such that g ( S T ) ∈ L 2 , we approximate g ( S T ) - E g ( S T ) by ∑ i = 1 n v i - 1 ( S τ i - S τ i - 1 ) where 0 = τ 0 ⩽ ⋯ ⩽ τ n = T is an increasing sequence of stopping times and the v i - 1 are F τ i - 1 -measurable random variables such that E v i - 1 2 ( S τ i - S τ i - 1 ) 2 ∞ ( ( F t ) t ∈ [ 0 , T ] is the augmentation of the natural filtration of the underlying Brownian motion). In case that g is not almost surely linear, we show that one gets a lower bound for the L 2 -approximation rate of 1 / n if one optimizes over all nets consisting of n + 1 stopping time…
American Option Pricing and Exercising with Transaction Costs
2005
In this paper we examine the problem of finding the reservation option prices and corresponding exercise policies of American options in a market with proportional transaction costs using the utility based approach proposed by Davis and Zariphopoulou (1995). We present a model where the option holder has a constant absolute risk aversion. We discuss the numerical algorithm and propose a new characterization of the option holder's value function. We suggest original discretization schemes for computing reservation prices and exercise policies of American options. The discretization schemes are implemented for the cases of American put and call options. We present the study of the optimal tra…
Performance of adaptive sample size adjustment with respect to stopping criteria and time of interim analysis
2006
The benefit of adjusting the sample size in clinical trials on the basis of treatment effects observed in interim analysis has been the subject of several recent papers. Different conclusions were drawn about the usefulness of this approach for gaining power or saving sample size, because of differences in trial design and setting. We examined the benefit of sample size adjustment in relation to trial design parameters such as 'time of interim analysis' and 'choice of stopping criteria'. We compared the adaptive weighted inverse normal method with classical group sequential methods for the most common and for optimal stopping criteria in early, half-time and late interim analyses. We found …
New approach to energy loss measurements
2002
Abstract A new approach to energy loss measurements is proposed. In the same experiment electronic stopping force (power) in gold, nickel, carbon, polycarbonate and Havar for 40 Ar, 28 Si, 16 O, 4 He and 1 H ions in the energy range 0.12–11 MeV/u has been measured. In this paper we give the full results for gold, nickel, and carbon and for 40 Ar, 16 O, 4 He and 1 H ions. Good agreement of the measured stopping force values for light ions with literature data is interpreted as the positive test of the experimental technique. The same technique used with heavy ions yields agreement with the published data only for energies above 1 MeV/u. At lower energies we observe progressively increasing d…
Optimal selection of the four best of a sequence
1993
We consider the situation in which the decision-maker is allowed to have four choices with purpose to choose exactly the four absolute best candidates fromN applicants. The optimal stopping rule and the maximum probability of making the right choice are given for largeN∈N, the maximum asymptotic value of the best choice being limN→∞P(win)≈0.12706.
Design, construction and cooling system performance of a prototype cryogenic stopping cell for the Super-FRS at FAIR
2015
A cryogenic stopping cell for stopping energetic radioactive ions and extracting them as a low energy beam was developed. This first ever cryogenically operated stopping cell serves as prototype device for the Low-Energy Branch of the Super-FRS at FAIR. The cell has a stopping volume that is 1 m long and 25 cm in diameter. Ions are guided by a DC field along the length of the stopping cell and by a combined RF and DC fields provided by an RE carpet at the exit-hole side. The ultra-high purity of the stopping gas required for optimum ion survival is reached by cryogenic operation. The design considerations and construction of the cryogenic stopping cell, as well as some performance character…
Rate capability of a cryogenic stopping cell for uranium projectile fragments produced at 1000 MeV/u
2016
At the Low-Energy Branch (LEB) of the Super-FRS at FAIR, projectile and fission fragments will be produced at relativistic energies, separated in-flight, energy-bunched, slowed down and thermalized in a cryogenic stopping cell (CSC) filled with ultra-pure He gas. The fragments are extracted from the stopping cell using a combination of DC and RF electric fields and gas flow. A prototype CSC for the LEB has been developed and successfully commissioned at the FRS Ion Catcher at GSI. Ionization of He buffer gas atoms during the stopping of energetic ions creates a region of high space charge in the stopping cell. The space charge decreases the extraction efficiency of stopping cells since the …
Magnetic Monopole Search with the Full MoEDAL Trapping Detector in 13 TeV pp Collisions Interpreted in Photon-Fusion and Drell-Yan Production
2019
MoEDAL is designed to identify new physics in the form of stable or pseudostable highly ionizing particles produced in high-energy Large Hadron Collider (LHC) collisions. Here we update our previous search for magnetic monopoles in Run 2 using the full trapping detector with almost four times more material and almost twice more integrated luminosity. For the first time at the LHC, the data were interpreted in terms of photon-fusion monopole direct production in addition to the Drell-Yan-like mechanism. The MoEDAL trapping detector, consisting of 794 kg of aluminum samples installed in the forward and lateral regions, was exposed to 4.0 fb$^{-1}$ of 13 TeV proton-proton collisions at the LHC…