Giant magnetoresistance through a single molecule

Magnetoresistance is a change in the resistance of a material system caused by an applied magnetic field. Giant magnetoresistance occurs in structures containing ferromagnetic contacts separated by a metallic non-magnetic spacer, and is now the basis of read heads for hard drives and for new forms of random access memory. Using an insulator (for example, a molecular thin film) rather than a metal as the spacer gives rise to tunnelling magnetoresistance, which typically produces a larger change in resistance for a given magnetic field strength, but also yields higher resistances, which are a disadvantage for real device operation. Here, we demonstrate giant magnetoresistance across a single, non-magnetic hydrogen phthalocyanine molecule contacted by the ferromagnetic tip of a scanning tunnelling microscope. We measure the magnetoresistance to be 60% and the conductance to be 0.26G(0), where G(0) is the quantum of conductance. Theoretical analysis identifies spin-dependent hybridization of molecular and electrode orbitals as the cause of the large magnetoresistance.     

Facultative skin pigmentation in caucasians: an objective biological indicator of lifetime exposure to ultraviolet radiation?

To investigate age and gender trends in facultative and constitutive skin pigmentation we measured skin pigmentation non-invasively and objectively by skin reflectance spectroscopy in 653 caucasians (336 females and 317 males; mean age 38 years, range 0-85) who were not using artificial tanning devices. In all subjects, measurements were performed in the late winter and pre-spring period at five sites exposed to ultraviolet (UV) radiation: the forehead, the upper chest, the upper back and the lateral and medial aspects of the upper arm, and in UV-unexposed buttock skin. Constitutive pigmentation at the buttocks was highest in the first years of life and then decreased substantially during the first two decades of life (P < 0.01). After the age of 25 years, buttock pigmentation remained at a constant level (P = 0.20). There was no gender difference in constitutive pigmentation. Facultative skin pigmentation increased with age for all the measured sites with the highest levels found at the lateral aspect of the upper arm. Based on observations in this study we propose the idea of a 'sun exposure index' (SEI) for individuals, based on objective measurements of skin pigmentation. The SEI is calculated as the increase in facultative pigmentation above the constitutive level and is expressed as a percentage of the constitutive level. The SEI appeared to be related to cumulative lifetime UV exposure and may be used in epidemiological research as an objective estimate of UV exposure at different body sites in caucasians.     

Epidural anaesthesia and spinal haematoma

PURPOSE: Haematoma formation in the spinal canal due to epidural anaesthesia is a very rare but serious complication. This paper presents a comprehensive review of case reports. SOURCE: Sampling of case reports over a 10 yr period, medline-research (1966-1995) and cross-check with former reviews. FINDINGS: Fifty-one confirmed spinal haematomas associated with epidural anaesthesia were found. Most were related to the insertion of a catheter, a procedure that was graded as difficult or traumatic in 21 patients. Other risk factors were: fibrinolytic therapy (n = 2), previously unknown spinal pathology (n = 2), low molecular weight heparin (n = 2), aspirin or other NSAID (n = 3), epidural catheter inserted during general anaesthesia (n = 3), thrombocytopenia (n = 5), ankylosing spondylitis (n = 5), preexisting coagulopathy (n = 14), and intravenous heparin therapy (n = 18). CONCLUSION: Coagulopathies or anticoagulant therapy (e.g., full heparinization) were the predominant risk factors, where-as low-dose heparin thromboprophylaxis or NSAID treatment was rarely associated with spinal bleeding complications. Ankylosing spondylitis was identified as a new, previously unreported risk factor. Analysis of reported clinical practice suggests an incidence of haematoma of 1:190,000 epidurals.     

Variability of practice and implicit motor learning.

The authors examined variable versus constant practice effects on implicit motor learning in continuous pursuit tracking. On every trial, two thirds of each trial consisted of random patterns, whereas one third was always repeated. The tracking patterns (including the repeated segment) were linearly scaled in absolute amplitude (Experiment 1) or overall speed (Experiments 1 and 2), with the scaling factors being either varied or constant across trials for different groups. The repeated segment was generally produced more accurately than the 2 random segments on retention tests and on transfer tests with novel scalings—and without participants' awareness of the repetition—suggesting that the repeated segment was learned implicitly. Also, learning was generally enhanced by variable practice, as compared with constant practice, suggesting that the advantages of variable over constant practice found in discrete tasks are generalizable to feedback-regulated tracking tasks. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Metastasis to the small intestine of malignant melanoma as a rare cause of intestinal hemorrhage

This is the case report of a 63 year old female patient, who was admitted to the hospital due to an unexplained anemia. A malignant melanoma of the cheek was excised four years previously (stage II, Clark level V, TNM classification: pT4, pNl, MO), followed by chemotherapy. By x-ray and CT examination an intestinal malignant growth was assumed. Laparotomy revealed a metastasis of the malignant melanoma, situated in the middle of the jejunum as cause of the occult bleeding. Complete resection of the tumor was successfully carried out. A second look laparotomy one year later revealed no further tumor growth in the abdominal cavity.     

Compilers and Computer Architecture

An examination of the relation between architecture and compiler design leads to several principles which can simplify compilers and improve the object code they produce.     

Selenium and its interrelatiosn with mercury in wholeblood and hair in an East Greenlandic population

138 Blood samples and 12 hair samples from the district of Angmagssalik, East Greenland, have been analysed for selenium and mercury. It was found that selenium like mercury, was absorbed in accordance with the amount of marine food eaten. The mean blood concentration in the group eating most marine food was 173 and 186 μg Hg/1 for men and women, respectively, while in the group eating the lowest quantity of marine food, the mean values were 86 and 118 μg Hg/1. In blood, the selenium and mercury did not correlate in individuals, but only in groups according to eating habits. On a molar basis, selenium is present in blood in excess as compared to mercury, while the opposite is the case for hair. It is concluded that only part of the selenium interacts with mercury, and that blood, but not hair, reflects present dietary intake. The rich supply of selenium in relation to mercury exposure through the traditional arctic food is probably able to alleviate the hazards from dietary mercury exposure.     

Computer Networks

Computer networks have the ability to bring the power of large machines to work on a single problem and to provide reliable computer services to large populations. They also may become an unmanageable structure that can cripple itself in a fashion akin to the great Northeast power failure in 1965. Imagine the following sequence: computer X does not have the sine subprogram but relies on computer Y for it; computer Y on the other hand solves the sine subprogram using the cosine subprogram which it doesn't have; computer Y therefore calls X for a cosine; X solves for cosine using sine which it asks Y for.& Of course, you say, no computer network would be so simplistic. But would you guarantee it could never happen for any set of computer resources among N computers-and that the network might not head for the buried recursive disaster like a lemming for a cliff?