Person to Person in Norway

While still in the midst of their study abroad experiences, students at Linfield College write reflective essays. Their essays address issues of cultural similarity and difference, compare lifestyles, mores, norms, and habits between their host countries and home, and examine changes in perceptions about their host countries and the United States. In this essay, Amber Hay describes her observations during her study abroad program at Telemark University College in Bø, Norway

Vasopressin V2 receptor antagonists in ADPKD:improving aquaretic side-effects and beyond

Autosomal dominant polycystic kidney disease is a hereditary disease that leads to the formation of numerous cysts in both kidneys of affected patients. These cysts destroy healthy kidney tissue, leading to kidney failure in the majority of patients around 60 years of age. A crucial hormone that is implicated in formation of these cysts is vasopressin. The first part of this thesis aims to identify factors that influence vasopressin, in order to potentially develop strategies that can slow down disease progression. For example, it was found that reduction of salt intake could potentially slow down kidney function decline. The second part of this thesis investigates the only effective drug that is available in polycystic kidney disease: the vasopressin antagonist tolvaptan. Tolvaptan blocks the hormone vasopressin, which leads to less cyst formation and slower kidney function decline. Unfortunately, tolvaptan also has side-effects: it causes massive urine production, up to 10 L per day. This thesis investigates whether this side-effect can be reduced. Potential strategies were investigated in mice with polycystic kidney disease, as well as in a clinical trial with patients. Three effective strategies were found. (1) Reduction of salt and protein intake. (2) The drug hydrochlorothiazide, which can reduce urine production by 25%. (3) The drug metformin, which can reduce urine production by 22%. The results of this thesis can help to make treatment with tolvaptan more tolerable, making it a better treatment option for patients with polycystic kidney disease

When topology triggers a phase transition

Two mathematical mechanisms, responsible for the generation of a thermodynamic singularity, are individuated. For a class of short-range, confining potentials, a topology change in some family of configuration space submanifolds is the only possible such mechanism. Two examples of systems in which the phase transition is not accompanied by a such topology change are discussed. The first one is a model with long-range interactions, namely the mean-field phi^4-model, the second example is a one-dimensional system with a non-confining potential energy function. For both these systems, the thermodynamic singularity is generated by a maximization over one variable (or one discrete index) of a smooth function, although the context in which the maximization occurs is very different.Comment: Talk given at the Next-SigmaPhi conference in Kolymbari, Crete, Greece, August 13-18, 200

Evaluating Human Performance for Image-Guided Surgical Tasks

The following work focuses on the objective evaluation of human performance for two different interventional tasks; targeted prostate biopsy tasks using a tracked biopsy device, and external ventricular drain placement tasks using a mobile-based augmented reality device for visualization and guidance. In both tasks, a human performance methodology was utilized which respects the trade-off between speed and accuracy for users conducting a series of targeting tasks using each device. This work outlines the development and application of performance evaluation methods using these devices, as well as details regarding the implementation of the mobile AR application. It was determined that the Fitts’ Law methodology can be applied for evaluation of tasks performed in each surgical scenario, and was sensitive to differentiate performance across a range which spanned experienced and novice users. This methodology is valuable for future development of training modules for these and other medical devices, and can provide details about the underlying characteristics of the devices, and how they can be optimized with respect to human performance

Environmental effects of genotoxins (eco-genotoxicology)

Genotoxic chemicals can damage the genetic material of humans as well as that of organisms living in the environment. With respect to adverse effects, alterations induced in the germ line, leading to alterations in the genetic make-up of populations, are of primary concern in ecosystems, because somatic changes, even if they lead to a loss of individuals, will not be critical in populations with a large reproductive surplus. This is different in human toxicology where genetic alterations in germ cells as well as in somatic cells of any individual are of concern. Increased frequencies of mutations and related genetic alterations in the gene pools of individual species or populations in ecosystems have to be judged against the background of spontaneous mutations that have enabled species to survive and adapt in changing environments since the beginning of life on our planet, and which have played an important role as the substrate for evolutionary developments. Examples of the selection of altered phenotypes (and genotypes) in response to environmental pollution and environmental stress are melanism in moth populations, metal resistance in plants, insecticide resistance in insects and malaria resistance in humans. Pollution, in general, can represent a stress factor selectively leading to a change in genetic make-up. In addition, environmental genotoxins can directly alter gene pools. A change in the genetic constitution may be advantageous for certain populations living in stressful conditions, but may present a disadvantage for others, including man. Examples are (i) the induction of (pesticide) resistance, (ii) the increased virulence of pathogens, (iii) alterations of host ranges of pathogenic forms or the appearance of new virus types and (iv) subtle changes in parasite—host or predator—prey relationships. Basically the release of genotoxins into the environment should be avoided because massive exposures may affect the reproductive capacity of many species, and modest exposures may lead to an enhanced instability of ecosystems and may provoke specific adaptations to stressful situations. Furthermore, the uncontrolled presence of genotoxins in any compartment of the natural environment is an unwanted situation, in particular also from a human point of view. In addition we need novel quantitative approaches in order to make quantitative risk estimates possibl

Insight into Resonant Activation in Discrete Systems

The resonant activation phenomenon (RAP) in a discrete system is studied using the master equation formalism. We show that the RAP corresponds to a non-monotonic behavior of the frequency dependent first passage time probability density function (pdf). An analytical expression for the resonant frequency is introduced, which, together with numerical results, helps understand the RAP behavior in the space spanned by the transition rates for the case of reflecting and absorbing boundary conditions. The limited range of system parameters for which the RAP occurs is discussed. We show that a minimum and a maximum in the mean first passage time (MFPT) can be obtained when both boundaries are absorbing. Relationships to some biological systems are suggested.Comment: 5 pages, 5 figures, Phys. Rev. E., in pres

A proof of the Kramers degeneracy of transmission eigenvalues from antisymmetry of the scattering matrix

In time reversal symmetric systems with half integral spins (or more concretely, systems with an antiunitary symmetry that squares to -1 and commutes with the Hamiltonian) the transmission eigenvalues of the scattering matrix come in pairs. We present a proof of this fact that is valid both for even and odd number of modes and relies solely on the antisymmetry of the scattering matrix imposed by time reversal symmetry.Comment: 2 page

Storage of classical information in quantum spins

Digital magnetic recording is based on the storage of a bit of information in the orientation of a magnetic system with two stable ground states. Here we address two fundamental problems that arise when this is done on a quantized spin: quantum spin tunneling and back-action of the readout process. We show that fundamental differences exist between integer and semi-integer spins when it comes to both, read and record classical information in a quantized spin. Our findings imply fundamental limits to the miniaturization of magnetic bits and are relevant to recent experiments where spin polarized scanning tunneling microscope reads and records a classical bit in the spin orientation of a single magnetic atom