Phase diagram of the 2D 4^4He in the density-temperature plane

Thin $^4$He films adsorbed to weakly attractive substrates form nearly 2D layers. We describe the vortices in 2D superfluid $^4$He like quasiparticles. With the aid of a variational many-body calculation we estimate their inertial mass and describe their interactions with the $^4$He particles and other vortices. Third sound measurements revealed anomalous behavior below the BKT-phase transition temperature. We ascribe this to the sound mode traveling in the fluid of vortex-antivortex pairs. These pairs forms a crystal (or liquid crystal) when the film thickness increases, the third sound mode splits into two separate modes as seen in experiments. Our many-body calculation predicts the critical density, at which the phase transition into the vortex-antivortex state at zero temperature occurs. We also describe the phase diagram of thin $^4$He films.Comment: Contribution paper to LT21 (to be published in Physica B

Structure of metastable 2D liquid helium

We present diffusion Monte Carlo (DMC) results on a new metastable, superfluid phase above the crystal ground state in two-dimensional 4He at densities > 0.065 1/A^2. The state is anisotropic with hexatic orbital order. This implies that the liquid--solid phase transition has two stages: A second order phase transition from the isotropic superfluid to the hexatic superfluid, followed by a first order transition that localizes atoms into the triangular crystal order. This metastable hexatic phase has finite condensate fraction and it provides a natural explanation for the superflow in the supersolid grain boundaries

Hole crystallization in semiconductors

When electrons in a solid are excited to a higher energy band they leave behind a vacancy (hole) in the original band which behaves like a positively charged particle. Here we predict that holes can spontaneously order into a regular lattice in semiconductors with sufficiently flat valence bands. The critical hole to electron effective mass ratio required for this phase transition is found to be of the order of 80.Comment: accepted for publication in J. Phys. A: Math. Ge

Quantum sticking, scattering and transmission of 4He atoms from superfluid 4He surfaces

We develop a microscopic theory of the scattering, transmission, and sticking of 4He atoms impinging on a superfluid 4He slab at near normal incidence, and inelastic neutron scattering from the slab. The theory includes coupling between different modes and allows for inelastic processes. We find a number of essential aspects that must be observed in a physically meaningful and reliable theory of atom transmission and scattering; all are connected with multiparticle scattering, particularly the possibility of energy loss. These processes are (a) the coupling to low-lying (surface) excitations (ripplons/third sound) which is manifested in a finite imaginary part of the self energy, and (b) the reduction of the strength of the excitation in the maxon/roton region

Geriatric Rehabilitation as an Integral Part of Geriatric Medicine in the Nordic Countries

Neðst á síðunni er hægt að nálgast greinina í heild sinni með því að smella á hlekkinn View/OpenObjective: Firstly to outline the theoretical and practical framework for geriatric rehabilitation in Iceland and other Nordic countries and secondly to survey the scientific medical publications for evidence based geriatric rehabilitation. Methods: Brain storming on geriatric rehabilitation in a working group of Nordic teachers in geriatric medicine. Papers on scientific programs for geriatric rehabilitation from Internet sources were collected and analyzed. All articles describing randomized studies in geriatric rehabilitation were selected for overview. The papers were divided into four groups according to diseases, infirmity and resource settings; 1) stroke, 2) hip-fractures, 3) acute admissions and 4) programs conducted in nursing homes, day hospitals and home services. Results: A spectrum of biological and social events creates the conditions underlying most causes for illness and disability in old people. The process of established geriatric services promotes the efficiency of geriatric rehabilitation. The literature survey included 27 scientific studies (8586 patients) on randomized studies with valid endpoints. Geriatric rehabilitation programs for stroke patients in geriatric settings, six studies (1138 patients), reduced mortality and the need for nursing home placement but the outcome for ADL. Function and length of stay was more variable between the studies. The outcome of geriatric rehabilitation was even more decisive in the randomized hip-fracture studies, six studies (2171 patients). Eight studies were found comparing the outcome between acute admission of frail elderly to either geriatric (GEMU, GRU) or general medical wards. The outcome as regards to mortality rate at one year, placement to a nursing home, physical function, contentment with services, readmission rate and cost was all significantly better in the geriatric settings. Internal comparisons of geriatric programs in nursing homes, day hospitals and in home service, seven studies (1261 patient), revealed some differences in outcomes in function, contentment and costs. Conclusions: Specialized geriatric rehabilitation is complicated but effective when properly performed. Interdisciplinary teamwork, targeting of patients, comprehensive assessment and intensive and patient-targeted rehabilitation seem to characterize the most effective programs. Rehabilitation of frail elderly people poses a major challenge for the future and has to be developed further for the sake of quality of life of elderly people as well as for economic reasons.Markmið: Að gera úttekt á öldrunarendurhæfingu á Íslandi og öðrum Norðurlöndum, marka hinn hugmyndafræðilega grunn, tengja hann norrænum veruleika og taka saman vísindalegar niðurstöður um árangur öldrunarendurhæfingar. Aðferð: Hugarflugsfundir vinnuhóps kennara í öldrunarlækningum um öldrunarendurhæfingu. Sértæk leit í helstu læknatímarita á Medline í greinum sem fjalla um aðferðir og meðferðarleiðir endurhæfingar fyrir aldraða á vísindalegan hátt. Um er að ræða samantekt á rannsóknum sem notast við slembiúrtök og taka til elstu aldurshópa. Greinunum var skipt niður í fjóra flokka eftir sjúkdómum, færni og staðsetningu; 1) heilablóðfall, 2) mjaðmarbrot, 3) bráðveikir og hrumir, 4) prógrömm á hjúkrunarheimilum, dagspítölum og í heimaþjónustu. Niðurstöður: Lífeðlisfræðilegir og félagslegir þættir marka veikindaferli og fötlun aldraðra. Verklag öldrunarþjónustunnar skiptir miklu um árangur öldrunarendurhæfingar. Leit í 27 tímaritsgreinum náði til 8586 sjúklinga en þær báru saman slembiúrtök og höfðu haldbærar viðmiðanir. Endurhæfing aldraðra heilablóðfallssjúklinga á öldrunarlækningadeild, sex rannsóknir (1138 sjúklingar), dró úr dánarlíkum og minnkaði þörf fyrir stofnanavist en breyting á mælanlegri færni og legudagafjöldi varð ekki afgerandi hjá öllum. Enn betri árangur náðist við endurhæfingu eftir mjaðmarbrot, sex rannsóknir (2171 sjúklingur). Átta rannsóknir (4016 sjúklingar) báru saman árangur öldrunarlækningadeilda borið saman við almennar lyflæknisdeildir í meðhöndlun bráðveikra og hrumra sjúklinga. Niðurstöður voru flestar afgerandi betri á öldrunarlækningadeildum hvað varðar dánartíðni að ári, vistun á hjúkrunarheimili, líkamlega færni, ánægju, endurinnlagnir og kostnað. Innbyrðis samanburður á endurhæfingaraðferðum fyrir aldraða á hjúkrunarheimilum, dagspítölum og í heimaþjónustu, sjö rannsóknir (1261 sjúklingur), sýndu mun á nokkrum viðmiðunum í færniþáttum, ánægju og kostnaði. Ályktanir: Sérhæfð endurhæfing aldraðra er flókin en skilar árangri þegar rétt er á haldið. Bestur árangur næst með fjölfaglegri teymisvinnu, val á þeim sjúklingum sem mestu áhættuna hafa, alhliða öldrunarmati og virkri og einstaklingsmiðaðri endurhæfingu. Endurhæfing á hrumu gömlu fólki er og verður vaxandi viðfangsefni fyrir heilbrigðisþjónustuna og mikilvægt að hún nái því markmiði að auka lífsgæði aldraðs fólks. Benda rannsóknir einnig til að við það skapist einnig efnahagslegur ávinningur fyrir land og þjóð

Stability of vortex lines in liquid 3He-4He mixtures at zero temperature

At low temperatures and 3He concentrations below 6.6 %, there is experimental evidence about the existence in liquid helium mixtures, of stable vortices with 3He-rich cores. When the system is either supersaturated or submitted to a tensile strength, vortices lose stability becoming metastable and eventually completely unstable, so that their cores freely expand. Within a density functional approach, we have determined the pressure-3He concentration curve along which this instability appears at zero temperature.Comment: Typeset using Revtex, 9 pages and 5 Postscript figure

A novel desmoplakin mutation causes dilated cardiomyopathy with palmoplantar keratoderma as an early clinical sign

Background PPKs represent a heterogeneous group of disorders with hyperkeratosis of palmar and/or plantar skin. PPK, hair shaft abnormalities, cardiomyopathy and arrhythmias can be caused by mutations in desmosomal genes, e.g. desmoplakin (DSP). PPK should trigger genetic testing to reveal mutations with possible related cardiac disease. Objectives To report a large multigenerational family with a novel DSP mutation associated with early-onset PPK and adult-onset cardiomyopathy and arrhythmias. Methods A custom-designed in-house panel of 35 PPK related genes was used to screen mutations in the index patient with focal PPK. The identified DSP mutation was verified by Sanger sequencing. DNA samples from 20 members of the large multigenerational family were sequenced for the DSP mutation. Medical records were reviewed. Clinical dermatological evaluation was performed, including light microscopy of hair samples. Cardiac evaluation included clinical examination, echocardiography, cardiac magnetic resonance imaging (CMR), electrocardiogram (ECG), Holter monitoring and laboratory tests. Results We identified a novel autosomal dominant truncating DSP c.2493delA p.(Glu831Aspfs*33) mutation associated with dilated cardiomyopathy (DCM) with arrhythmia susceptibility and focal PPK as an early cutaneous sign. The mutation was found in nine affected family members, but not in any unaffected members. Onset of dermatological findings preceded cardiac symptoms which were variable and occurred at adult age. Conclusions We report a novel truncating DSP mutation causing focal PPK with varying severity and left ventricular dilatation and ventricular extrasystoles. This finding emphasizes the importance of genetic diagnosis in patients with PPK for clinical counselling and management of cardiomyopathies and arrhythmias.Peer reviewe

Dipolar clusters and ferroelectricity in high Tc superconductors

Electronic version of an article published as International Journal of Modern Physics B, 2015, 29, 1542002. DOI:10.1142/S0217979215420023 © [copyright World Scientific Publishing Company] http://www.worldscientific.com/worldscinet/ijmpbIn this paper, we show that doping of hole charge carriers induces formation of resonance plaquettes (RPs) having electric dipolar moments and fluctuating stripes in cuprates. A single RP is created by many-body interactions between the dopant ion or a charge fluctuation outside and holes inside the CuO plane. In such a process, Coulomb interacting holes in the CuO plane are self-organized into four-particles resonance valence bond plaquettes bound with dopants or polarons located in the spacer layer between CuO planes. Such RPs have ordered and disordered phases. They are ordered into charge density waves (CDW) or stripes only at certain conditions. The lowest energy of the ordered phase corresponds to a local antiferroelectric ordering. The RPs mobility is very low at low temperatures and they are bound into dipole–dipole pairs. Electromagnetic radiation interacts strongly with RPs electric dipoles and when the sample is subjected to it, the mobility changes significantly. This leads to a fractal growth of dipolar RP clusters. The existence of electric dipoles and CDW reveal a series of new phenomena such as ferroelectricity, strong light and microwave absorption and the field induced superconductivity

Quasicondensate and superfluid fraction in the 2D charged-boson gas at finite temperature

The Bogoliubov - de Gennes equations are solved for the Coulomb Bose gas describing a fluid of charged bosons at finite temperature. The approach is applicable in the weak coupling regime and the extent of its quantitative usefulness is tested in the three-dimensional fluid, for which diffusion Monte Carlo data are available on the condensate fraction at zero temperature. The one-body density matrix is then evaluated by the same approach for the two-dimensional fluid with e^2/r interactions, to demonstrate the presence of a quasi-condensate from its power-law decay with increasing distance and to evaluate the superfluid fraction as a function of temperature at weak coupling.Comment: 9 pages, 2 figure