Theoretical surgery: a new specialty in operative medicine

Theoretical surgery is defined as a nonoperative decision analysis and clinical and basic research supporting system for surgery. It developed to meet the needs of academic surgeons to coordinate communication with basic science disciplines. This article summarizes the development of this idea at the University of Marburg where theoretical surgery has reached departmental and institutional proportions. Its objectives and methods are described. Central to its operation are permanent working teams of 2 clinical surgeons, 1 basic scientist (theoretical surgeon), 1-2 technicians, and 1-2 students focusing on one problem in a joint interdisciplinary manner. Decision analysis with classification methods and the creation of decision trees and algorithms are central to the operation of this experiment. Lessons learned from this academic experiment and the accomplishments during the past 20 years are summarized on 3 levels of efficacy: performance, changing strategies, and outcome

Mass administrations of antimalarial drugs.

Administration of antimalarial drugs to whole populations has been used as a malaria-control measure for more than 70 years. Drugs have been administered either directly as a full therapeutic course of treatment or indirectly through the fortification of salt. Mass drug administrations (MDAs) were generally unsuccessful in interrupting transmission but, in some cases, had a marked effect on parasite prevalence and on the incidence of clinical malaria. MDAs are likely to encourage the spread of drug-resistant parasites and so have only a limited role in malaria control. They could have a part to play in the management of epidemics and in the control of malaria in areas with a short transmission season. To reduce the risk of spreading drug resistance, MDAs should use more than one drug and, preferably include a drug, such as an artemisinin, which has a gametocidal effect

Thermal expansion of the spin-1/2 Heisenberg-chain compound Cu(C4_4H4_4N2_2)(NO3_3)2_2

Compounds containing magnetic subsystems representing simple model spin systems with weak magnetic coupling constants are ideal candidates to test theoretical predictions for the generic behavior close to quantum phase transitions. We present measurements of the thermal expansion and magnetostriction of the spin-1/2-chain compound copper pyrazine dinitrate Cu(C$_4$H$_4$N$_2$)(NO$_3$)$_2$. Of particular interest is the low-temperature thermal expansion close to the saturation field $H_c \simeq 13.9 \mathrm{T}$, which defines a quantum phase transition from the gapless Luttinger liquid state to the fully saturated state with a finite excitation gap. We observe a sign change of the thermal expansion for the different ground states, and at the quantum critical point $H_c$ the low-temperature expansion approaches a $1/\sqrt{T}$ divergence. Thus, our data agree very well with the expected quantum critical behaviour.Comment: 4 pages, 3 figures; to appear in the proceedings of the ICM 09 held in Karlsruhe, German

Solving the riddle of codon usage preferences: a test for translational selection

Translational selection is responsible for the unequal usage of synonymous codons in protein coding genes in a wide variety of organisms. It is one of the most subtle and pervasive forces of molecular evolution, yet, establishing the underlying causes for its idiosyncratic behaviour across living kingdoms has proven elusive to researchers over the past 20 years. In this study, a statistical model for measuring translational selection in any given genome is developed, and the test is applied to 126 fully sequenced genomes, ranging from archaea to eukaryotes. It is shown that tRNA gene redundancy and genome size are interacting forces that ultimately determine the action of translational selection, and that an optimal genome size exists for which this kind of selection is maximal. Accordingly, genome size also presents upper and lower boundaries beyond which selection on codon usage is not possible. We propose a model where the coevolution of genome size and tRNA genes explains the observed patterns in translational selection in all living organisms. This model finally unifies our understanding of codon usage across prokaryotes and eukaryotes. Helicobacter pylori, Saccharomyces cerevisiae and Homo sapiens are codon usage paradigms that can be better understood under the proposed model

From the Jordan product to Riemannian geometries on classical and quantum states

The Jordan product on the self-adjoint part of a finite-dimensional $C^{*}$-algebra $\mathscr{A}$ is shown to give rise to Riemannian metric tensors on suitable manifolds of states on $\mathscr{A}$, and the covariant derivative, the geodesics, the Riemann tensor, and the sectional curvature of all these metric tensors are explicitly computed. In particular, it is proved that the Fisher--Rao metric tensor is recovered in the Abelian case, that the Fubini--Study metric tensor is recovered when we consider pure states on the algebra $\mathcal{B}(\mathcal{H})$ of linear operators on a finite-dimensional Hilbert space $\mathcal{H}$, and that the Bures--Helstrom metric tensors is recovered when we consider faithful states on $\mathcal{B}(\mathcal{H})$. Moreover, an alternative derivation of these Riemannian metric tensors in terms of the GNS construction associated to a state is presented. In the case of pure and faithful states on $\mathcal{B}(\mathcal{H})$, this alternative geometrical description clarifies the analogy between the Fubini--Study and the Bures--Helstrom metric tensor.Comment: 32 pages. Minor improvements. References added. Comments are welcome

Similarity of percolation thresholds on the hcp and fcc lattices

Extensive Monte-Carlo simulations were performed in order to determine the precise values of the critical thresholds for site ($p^{hcp}_{c,S} = 0.199 255 5 \pm 0.000 001 0$) and bond ($p^{hcp}_{c,B} = 0.120 164 0 \pm 0.000 001 0$) percolation on the hcp lattice to compare with previous precise measuremens on the fcc lattice. Also, exact enumeration of the hcp and fcc lattices was performed and yielded generating functions and series for the zeroth, first, and second moments of both lattices. When these series and the values of $p_c$ are compared to those for the fcc lattice, it is apparent that the site percolation thresholds are different; however, the bond percolation thresholds are equal within error bars, and the series only differ slightly in the higher order terms, suggesting the actual values are very close to each other, if not identical.Comment: 10 pages, 4 figures, submitted to J. Stat. Phy

Electron-correlation driven capture and release in double quantum dots

We recently predicted that the interatomic Coulombic electron capture (ICEC) process, a long-range electron correlation driven capture process, is achievable in gated double quantum dots (DQDs). In ICEC an incoming electron is captured by one QD and the excess energy is used to remove an electron from the neighboring QD. In this work we present systematic full three-dimensional electron dynamics calculations in quasi-one dimensional model potentials that allow for a detailed understanding of the connection between the DQD geometry and the reaction probability for the ICEC process. We derive an effective one-dimensional approach and show that its results compare very well with those obtained using the full three-dimensional calculations. This approach substantially reduces the computation times. The investigation of the electronic structure for various DQD geometries for which the ICEC process can take place clarify the origin of its remarkably high probability in the presence of two-electron resonances

Controlled energy-selected electron capture and release in double quantum dots

Highly accurate quantum electron dynamics calculations demonstrate that energy can be efficiently transferred between quantum dots. Specifically, in a double quantum dot an incoming electron is captured by one dot and the excess energy is transferred to the neighboring dot and used to remove an electron from this dot. This process is due to long-range electron correlation and shown to be operative at rather large distances between the dots. The efficiency of the process is greatly enhanced by preparing the double quantum dot such that the incoming electron is initially captured by a two-electron resonance state of the system. In contrast to atoms and molecules in nature, double quantum dots can be manipulated to achieve this enhancement. This mechanism leads to a surprisingly narrow distribution of the energy of the electron removed in the process which is explained by resonance theory. We argue that the process could be exploited in practice.Comment: Lette