Uppsala University

About: Uppsala University is a education organization based out in Uppsala, Sweden. It is known for research contribution in the topics: Population & Insulin. The organization has 36485 authors who have published 107509 publications receiving 4220668 citations. The organization is also known as: Uppsala universitet & uu.se.

Origin of the Invar effect in iron–nickel alloys

Abstract: In 1897 Guillaume1 discovered that face-centred cubic alloys of iron and nickel with a nickel concentration of around 35 atomic per cent exhibit anomalously low (almost zero) thermal expansion over a wide temperature range. This effect, known as the Invar effect, has since been found in various ordered and random alloys and even in amorphous materials2. Other physical properties of Invar systems, such as atomic volume, elastic modulus, heat capacity, magnetization and Curie (or Neel) temperature, also show anomalous behaviour. Invar alloys are used in instrumentation, for example as hair springs in watches. It has long been realized that the effect is related to magnetism2,3; but a full understanding is still lacking. Here we present ab initio calculations of the volume dependences of magnetic and thermodynamic properties for the most typical Invar system, a random face-centred cubic iron–nickel alloy, in which we allow for non-collinear spin alignments—that is, spins that may be canted with respect to the average magnetization direction. We find that the magnetic structure is characterized, even at zero temperature, by a continuous transition from the ferromagnetic state at high volumes to a disordered non-collinear configuration at low volumes. There is an additional, comparable contribution to the net magnetization from the changes in the amplitudes of the local magnetic moments. The non-collinearity gives rise to an anomalous volume dependence of the binding energy, and explains other peculiarities of Invar systems.

Age-related cognitive deficits mediated by changes in the striatal dopamine system.

Abstract: OBJECTIVE: The study examined the influence of losses in dopaminergic function on age-related cognitive deficits. METHOD: Eleven healthy subjects (21–68 years of age) completed a set of cognitive tasks used to assess perceptual speed and episodic memory. D2 receptor binding was measured in the caudate and the putamen by using positron emission tomography. RESULTS: A gradual age-related deterioration was found for all cognitive tasks and for D2 binding in both striatal structures. Statistical control of D2 binding eliminated the age-related cognitive variation, whereas residual effects of D2 binding were seen after the analysis controlled for age. CONCLUSIONS: D2 receptor binding is a more important factor than chronological age in accounting for variation in cognitive performance across the adult lifespan. Changes in dopaminergic neurotransmission play an important role in aging-related cognitive decline.

Analysing real-time communications: controller area network (CAN)

Abstract: The increasing use of communication networks in time-critical applications presents engineers with fundamental problems with the determination of response times of communicating distributed processes. Although there has been some work on the analysis of communication protocols, most of this is for idealised networks. Experience with single-processor scheduling analysis has shown that models which abstract away from implementation details are at best very pessimistic, and at worst lead to an unschedulable system being deemed schedulable. In this paper, we derive an idealised scheduling analysis for the CAN real-time bus, and then study two actual interface chips to see how the analysis can be applied. >

Controlling cold atoms using nanofabricated surfaces: atom chips

Abstract: Atoms can be trapped and guided using nanofabricated wires on surfaces, achieving the scales required by quantum information proposals. These atom chips form the basis for robust and widespread applications of cold atoms ranging from atom optics to fundamental questions in mesoscopic physics, and possibly quantum information systems.

Extension of functions satisfying lipschitz conditions

Abstract: Le t F be a compac t set in Euc l idean n-space RL Suppose t h a t the funct ion ~(P) is def ined on F and t h a t i t satisfies a Lipschi tz condit ion. 1 I t is known t h a t ~0 can be e x t e n d e d to R ~ in such a w a y t h a t the new funct ion / satisfies t he same Lipsehi tz condit ion. An expl ic i t cons t ruc t ion was given in [1], where even more genera l s i tuat ions were t r ea t ed . I t is ea sy to give uppe r and lower bounds for the solutions. W e shal l do this, and also discuss quest ions of uniqueness. I t t u rns out t h a t a l l solut ions agree on a set E which has a ve ry s imple s t ruc ture (Theorem 2). I n ana logy wi th the t r e a t m e n t in [2] a n d [3], we shal l consider a subclass of solut ions (called absolu te minimals) which have the add i t i ona l p r o p e r t y of being solut ions of a corresponding p rob lem on each subregion of R ~ F . The pa r t i a l d i f ferent ia l equa t ion ~ . j=l, tx~ r tx~xj = 0 is de r ived in a pu re ly fo rmal m a n n e r and i t t u rns out t h a t a smooth funct ion satisfies th is equa t ion if and on ly if i t is an absolu te min ima l (Theorem 8). W e shal l also give an exis tence proof for abso lu te minima]s. I n a l a t e r paper , the two-d imens iona l case, a n d in pa r t i cu l a r the d i f ferent ia l equat ion r = 0, more r162 r tzu +Ca tuu will be s tud ied closely.