Theoretical study of kinks on screw dislocation in silicon

Theoretical calculations of the structure, formation and migration of kinks on a non-dissociated screw dislocation in silicon have been carried out using density functional theory calculations as well as calculations based on interatomic potential functions. The results show that the structure of a single kink is characterized by a narrow core and highly stretched bonds between some of the atoms. The formation energy of a single kink ranges from 0.9 to 1.36 eV, and is of the same order as that for kinks on partial dislocations. However, the kinks migrate almost freely along the line of an undissociated dislocation unlike what is found for partial dislocations. The effect of stress has also been investigated in order to compare with previous silicon deformation experiments which have been carried out at low temperature and high stress. The energy barrier associated with the formation of a stable kink pair becomes as low as 0.65 eV for an applied stress on the order of 1 GPa, indicating that displacements of screw dislocations likely occur via thermally activated formation of kink pairs at room temperature

On implicational bases of closure systems with unique critical sets

We show that every optimum basis of a finite closure system, in D.Maier's sense, is also right-side optimum, which is a parameter of a minimum CNF representation of a Horn Boolean function. New parameters for the size of the binary part are also established. We introduce a K-basis of a general closure system, which is a refinement of the canonical basis of Duquenne and Guigues, and discuss a polynomial algorithm to obtain it. We study closure systems with the unique criticals and some of its subclasses, where the K-basis is unique. A further refinement in the form of the E-basis is possible for closure systems without D-cycles. There is a polynomial algorithm to recognize the D-relation from a K-basis. Thus, closure systems without D-cycles can be effectively recognized. While E-basis achieves an optimum in one of its parts, the optimization of the others is an NP-complete problem.Comment: Presented on International Symposium of Artificial Intelligence and Mathematics (ISAIM-2012), Ft. Lauderdale, FL, USA Results are included into plenary talk on conference Universal Algebra and Lattice Theory, June 2012, Szeged, Hungary 29 pages and 2 figure

Dynamics of Selected Biomarkers in Cerebrospinal Fluid During Complex Endovascular Aortic Repair – A Pilot Study

INTRODUCTION: Ischemic spinal cord injury (SCI) is a serious complication of complex aortic repair. Prophylactic cerebrospinal fluid (CSF) drainage, used to decrease lumbar cerebrospinal fluid (CSF) pressure, enables monitoring of CSF biomarkers that may aid in detecting impending SCI. We hypothesized that biomarkers, previously evaluated in traumatic SCI and brain injury, would be altered in CSF over time following complex endovascular aortic repair (cEVAR). OBJECTIVES: To examine if a chosen cohort of CSF biomarker correlates to SCI and warrants further research. METHODS: A prospective observational study on patients undergoing cEVAR with extensive aortic coverage. Vital parameters and CSF samples were collected on ten occasions during 72 hours post-surgery. A panel of ten biomarkers were analyzed (Neurofilament Light Polypeptide (NFL), Tau, Glial Fibrillary Acidic Protein (GFAP), Soluble Amyloid Precursos Protein (APP) α and β, Amyloid β 38, 40 and 42 (Aβ38, 40 and 42), Chitinase-3-like protein 1 (CHI3LI or YKL-40), Heart-type fatty acid binding protein (H-FABP).). RESULTS: Nine patients (mean age 69, 7 males) were included. Median total aortic coverage was 68% [33, 98]. One patient died during the 30-day post-operative period. After an initial stable phase for the first few postoperative hours, most biomarkers showed an upward trend compared with baseline in all patients with >50% increase in value for NFL in 5/9 patients, in 7/9 patients for Tau and in 5/9 patients for GFAP. One patient developed spinal cord and supratentorial brain ischemia, confirmed with MRI. In this case, NF-L, GFAP and tau were markedly elevated compared with non-SCI patients (maximum increase compared with baseline in the SCI patient versus mean value of the maximal increase for all other patients: NF-L 367% vs 79%%, GFAP 95608% versus 3433%, tau 1020% vs 192%). CONCLUSION: . This study suggests an increase in all ten studied CSF biomarkers after coverage of spinal arteries during endovascular aortic repair. However, the pilot study was not able to establish a specific correlation between spinal fluid biomarker elevation and clinical symptoms of SCI due to small sample size and event rate

Perennial Lymegrass (Leymus arenarius and L. mollis) as Potential Crop Species for Northern Latitudes

The aim of the present study is to improve the perennial lymegrass (L. arenarius and L. mollis) for cultivation as potential cereal crop for Iceland as well as for other regions of native lymegrass distribution. The study will also provide cereal breeders with broader genetic resource containing several characters of the wild species such as tolerance to extreme environments and perhaps resistance to pathological diseases

Spatial genetic structure of the sea sandwort (<i>Honckenya peploides</i>) on Surtsey:an immigrant's journey

Sea sandwort (Honckenya peploides) was one of the first plants to successfully colonize and reproduce on the volcanic island Surtsey, formed in 1963 off the southern coast of Iceland. Using amplified fragment length polymorphic (AFLP) markers, we examined levels of genetic variation and differentiation among populations of H. peploides on Surtsey in relation to populations on the nearby island Heimaey and from the southern coast of Iceland. Selected populations from Denmark and Greenland were used for comparison. In addition, we tested whether the effects of isolation by distance could be seen in the Surtsey populations. Using two primer combinations, we obtained 173 AFLP markers from a total of 347 plant samples. The resulting binary matrix was then analysed statistically. The main results include the following: (i) Surtsey had the highest proportion of polymorphic markers as well as a comparatively high genetic diversity (55.5% proportion of polymorphic loci, PLP; 0.1974 HE) and Denmark the lowest (31.8% PLP; 0.132 HE), indicating rapid expansion during an early stage of population establishment on Surtsey and/or multiple origins of immigrants; (ii) the total genetic differentiation (FST) among Surtsey (0.0714) and Heimaey (0.055) populations was less than half of that found among the mainland populations in Iceland (0.1747), indicating substantial gene flow on the islands; (iii) most of the genetic variation (79%, p < 0.001) was found within localities, possibly due to the outcrossing and subdioecious nature of the species; (iv) a significant genetic distance was found within Surtsey, among sites, and this appeared to correlate with the age of plant colonization; and (v) the genetic structure analysis indicated multiple colonization episodes on Surtsey, whereby H. peploides most likely immigrated from the nearby island of Heimaey and directly from the southern coast of Iceland

Orbital-optimized Density Functional Calculations of Molecular Rydberg Excited States with Real Space Grid Representation and Self-Interaction Correction

Density functional calculations of Rydberg excited states up to high energy are carried out for several molecules using an approach where the orbitals are variationally optimized by converging on saddle points on the electronic energy surface within a real space grid representation. Remarkably good agreement with experimental estimates of the excitation energy is obtained using the generalized gradient approximation (GGA) functional of Perdew, Burke and Ernzerhof (PBE) when Perdew-Zunger self-interaction correction is applied in combination with complex-valued orbitals. Even without the correction, the PBE functional gives quite good results despite the fact that corresponding Rydberg virtual orbitals have positive energy in the ground state calculation. Results obtained using the TPSS and r2SCAN meta-GGA functionals are also presented, but they do not provide a systematic improvement over the results from the uncorrected PBE functional. The grid representation combined with the projector augmented-wave approach gives a simpler and better representation of the diffuse Rydberg orbitals than a linear combination of atomic orbitals with commonly used basis sets, the latter leading to an overestimation of the excitation energy due to confinement of the excited states.Comment: 34 pages, 8 figure

Survival and causes of death in children diagnosed with cancer in Iceland 1981-2006

Neðst á síðunni er hægt að nálgast greinina í heild sinni með því að smella á hlekkinn Skoða/Opna(view/open)OBJECTIVE: Of children diagnosed with cancer, approximately one fourth die of the disease or disease related complications. The aim of this study was to investigate survival and causes of death in children with cancer in Iceland. METHODS: This study is retrospective; population based and includes all children, less than 18 years of age, diagnosed with cancer in Iceland from 1981 to 2006. Information was extracted from the Icelandic Cancer Registry, patients hospital records and data from Statistics Iceland. RESULTS: Of 279 children diagnosed with cancer in the research period 215 were alive at the end of 2008. The overall 5-year survival was 81.2% and 10-year survival was 76.7%. There was not a significant survival difference with respect to age at diagnosis, year of diagnosis, gender or geographical residence. The small cohort size could be the explanation. Eleven individuals developed secondary neoplasm, eight of whom died. Sixteen of the 64 nonsurvivors were treated with curative intent until death, 12 of them died of therapy related complications. CONCLUSIONS: Survival rate in childhood cancer in Iceland is comparable to other Western countries. As previously reported, prognosis of patients with secondary neoplasm is unfavorable. Therapy related complications are the most common cause of death in patients treated with curative intent.Inngangur: Um fjórðungur barna sem greinist með krabbamein deyr vegna sjúkdóms síns eða meðferðartengdra fylgikvilla. Tilgangur rannsóknarinnar var að kanna lifun og dánarorsakir barna sem greinst hafa með krabbamein á Íslandi. Aðferðir: Rannsóknin var afturskyggn, lýðgrunduð og náði til allra einstaklinga yngri en 18 ára sem greindust með krabbamein á Íslandi frá upphafi árs 1981 til loka ársins 2006. Upplýsingum var safnað frá Krabbameinsskrá Íslands, sjúkraskrám og Hagstofu Íslands. Niðurstöður: Á rannsóknartímabilinu greindust 279 börn með krabbamein á Íslandi. Af þeim voru 215 á lífi í lok árs 2008. Á tímabilinu var fimm ára lifun 81,2% og 10 ára lifun 76,7%. Ekki var marktækur munur á lifun milli kynja, greiningartímabila, aldurs eða búsetu. Gæti það skýrst af smæð þýðisins. Lifun var mismunandi eftir krabbameinstegundum. Ellefu einstaklingar greindust síðar með meðferðartengd krabbamein, átta þeirra létust. Sextán þeirra 64 sem létust voru í læknandi meðferð fram að andláti. Var dánarorsök meðferðartengdir fylgikvillar hjá 12 úr þeim hópi. Ályktun: Horfur barna og unglinga á Íslandi með krabbamein eru sambærilegar við önnur vestræn ríki. Horfur eru mun verri í meðferðartengdum krabbameinum samanborið við frumkrabbamein. Meðferðartengdir fylgikvillar eru algengasta dánarorsök ef krabbameinsmeðferð er gefin með læknanlegum tilgangi

Childhood cancer in Iceland 1981-2006

Neðst á síðunni er hægt að nálgast greinina í heild sinni með því að smella á hlekkinn Skoða/Opna(view/open)BACKGROUND: Childhood cancer is the second most common cause of death in children. The aim of this study was to gather epidemiological information on childhood cancer in Iceland. METHODS: The study was population based and included all children younger than 18 years of age, diagnosed with cancer in Iceland from 1981 to 2006. Information was extracted from the Icelandic Cancer Registry and patient hospital records. RESULTS: During the study period 288 cancer cases were diagnosed in 279 children, 10 cases were secondary neoplasms. Age standardized incidence was 16.1 per 100.000 (95% CI 13,6-18,6) for boys and 12.8 per 100.000 (95% CI 10,5-15,0) for girls. There was no significant difference in the incidence rate between the first and second half of the study period. For children aged 0-14 years, the age standardized incidence was 13.6 per 100.000. The incidence was highest in the 0-4 year age group (17.3 per 100.000) and in the 15-17 year age group (19.6 per 100.000). Brain tumors (27.1%) and leukemia (25.0%) were the most common cancer groups diagnosed. Lymphoid leukemia was the most common cancer type (17.9%) and astrocytoma (13.1%) came second. CONCLUSIONS: The incidence of childhood cancer in Iceland is similar to other Western countries. Long-term follow-up is very important in childhood cancer survivors.Inngangur: Krabbamein er næst algengasta dánarorsök barna á eftir slysum. Tilgangur rann-sóknarinnar var að kanna nýgengi krabbameina hjá börnum á Íslandi.
 Aðferðir: Rannsóknin var lýðgrunduð og náði til allra <18 ára sem greindust með krabbamein á Íslandi frá upphafi árs 1981 til ársloka 2006. Upplýsingum var safnað frá Krabbameinsskrá Íslands og úr sjúkraskrám.
 Niðurstöður: Alls greindust 288 krabbameinstilfelli á tímabilinu hjá 279 börnum. Í 10 tilvikum var um meðferðartengd krabbamein að ræða. Árlegt aldursstaðlað nýgengi hjá drengjum var 16,1 af 100.000 (95% CI; 13,6-18,6) en hjá stúlkum 12,8 af 100.000 (95% CI; 10,5-15,0) en ekki var marktækur munur á nýgengi milli fyrri og seinni hluta rannsóknartímabilsins. Fyrir aldursbilið 0-14 ára var árlegt aldursstaðlað nýgengi 13,6 af 100.000. Miðtaugakerfisæxli og hvítblæði voru samanlagt 52,1% allra krabbameinstilvika. Algengasta grein-ingin var bráða eitilfrumuhvítblæði (17,9%) og stjarnfrumnaæxli (13,1%) næstalgengust. Nýgeng-ið var hæst hjá aldursbilunum 0-4 ára (17,3 af 100.00) og 15-17 ára (19,6 af 100.000). Tíu börn voru með þekkta meðfædda áhættuþætti.
 Ályktun: Nýgengi krabbameina hjá börnum á Íslandi er sambærilegt við nágrannalöndin. Mikilvægt er að fylgja vel eftir börnum sem gengið hafa í gegnum krabbameinsmeðferð og þeim sem hafa þekkta meðfædda áhættuþætti.