bluuebunny/crossref_metadata_2025 huggingface dataset:
Bipolar resistive switching with self-rectifying effects in Al/ZnO/Si structure
Authors: Chen C. , Pan F. , Wang Z. S. , Yang J. , Zeng F.
Published: January 2012

We report the electrical characteristics of room-temperature-fabricated Al/ZnO/Si memory devices. Stable and reproducible clockwise bipolar resistive switching phenomena with self-rectifying effects in the low resistance state were observed in this complementary metal oxide semiconductor compatible memory structure. The current-voltage curve in different temperatures and the corresponding Arrhenius plot confirm the semiconducting conduction behavior of both the high resistance state and the low resistance state. The conduction mechanisms are explained by the Poole-Frenkel emission and space-charge-limited conduction mechanisms for the high resistance state and the low resistance state, respectively. It is proposed that the resistive switching originates from the formation and dissolution of the AlOx barrier layer which are induced by the migration of the oxygen ions.
Observing “quantized” conductance steps in silver sulfide: Two parallel resistive switching mechanisms
Authors: Wagenaar Jelmer J. T. , Morales-Masis Monica , van Ruitenbeek Jan M.
Published: January 2012

We demonstrate that it is possible to distinguish two conductance switching mechanisms in silver sulfide devices at room temperature. Experiments were performed using a Ag2S thin film deposited on a wide Ag bottom electrode, which was contacted by the Pt tip of a scanning tunneling microscope. By applying a positive voltage on the silver electrode, the conductance is seen to switch to a state having three orders of magnitude higher conductance, which is related to the formation of a conductive path inside the Ag2S thin film. We argue this to be composed of a metallic silver nanowire accompanied by a modification of the surrounding lattice structure. Metallic silver nanowires decaying after applying a negative voltage allow observing conductance steps in the breaking traces characteristic for atomic-scale contacts, while the lattice structure deformation is revealed by gradual and continuously decreasing conductance traces.
Simulation of multilevel switching in electrochemical metallization memory cells
Authors: Menzel Stephan , Böttger Ulrich , Waser Rainer
Published: January 2012

We report on a simulation model for bipolar resistive switching in cation-migration based memristive devices. The model is based on the electrochemical driven growth and dissolution of a metallic filament. The origin of multilevel switching is proposed to be direct tunneling between the growing filament and the counter electrode. An important result of our parameter simulation studies is that different materials show the same experimental multilevel behavior. Our model fully reproduces the experimental data and allows for an explanation of the transition from bipolar to nonpolar switching.
Strain in free standing CdSe/CdS core-shell nanorods
Authors: Rajadell F. , Royo M. , Planelles J.
Published: January 2012

The main characteristic strain trends in free-standing II–VI wurtzite semiconductor nanorods coated with a few-monolayers shell are reported. Calculations for different aspect ratios and shell thicknesses show that these are key factors for the strength of strain components that can even change their sign. Strain in core-shell nanorods with few monolayers coating is strong and qualitatively different from that of buried dots. Hexagonal symmetry compared to cubic and isotropic approximations reveals that, with the appropriate parameters, isotropic strain mimics very well the strain distributions of wurtzite core-shell nanorods.
Understanding of the development of in-plane residual stress in sol-gel-derived metal oxide thin films
Authors: Ohno Kentaro , Uchiyama Hiroaki , Kozuka Hiromitsu
Published: January 2012

The in-plane residual stress in thin films greatly affects their properties and functionality as well as the substrate bending, and hence is an important factor to be controlled. In order to obtain general knowledge on the development of residual stress in sol-gel-derived oxide thin films, the in-plane residual stress was measured for yttria stabilized zirconia gel films on Si(100) wafers as a function of firing temperature by measuring the substrate curvature. The films showed a rather complex variation in residual stress, and the mechanism of the residual stress evolution was discussed, referencing the intrinsic stress and the x-ray diffraction data. At low annealing temperatures of 100–200 °C, the residual tensile stress decreased and became compressive partially due to the structural relaxation occurring during cooling. When the firing temperature was increased over 200 °C, the residual stress turned tensile, and increased with increasing annealing temperature, which was attributed to the increase in intrinsic stress due to film densification as well as to the reduced structural relaxation due to the progress of densification. The residual tensile stress slightly decreased at firing temperatures of 500–600 °C, which was attributed to the reduction in intrinsic stress due to thermally activated atomic diffusion as well as to emergence of thermal stress. At firing temperature over 600 °C, the residual tensile stress increased again, which was attributed to the increase in thermal stress generated during cooling due to the increased Young’s modulus of the film. Although appearing to be complicated, the whole variation of residual stress with firing temperature could be understood in terms of film densification, structural relaxation, atomic diffusion, progress of crystallization and thermal strain. The illustration presented in the work may provide a clear insight on how the residual stress could be developed in a variety of functional sol-gel-derived, crystalline oxide thin films.
S···X halogen bonds and H···X hydrogen bonds in H2CS–XY (XY = FF, ClF, ClCl, BrF, BrCl, and BrBr) complexes: Cooperativity and solvent effect
Authors: Li Qingzhong , Li Ran , Zhou Zhongjun , Li Wenzuo , Cheng Jianbo
Published: January 2012

Using ab initio calculations, we have studied the structures, properties, and nature of halogen bonds in H2CS–XY (XY = FF, ClF, ClCl, BrF, BrCl, and BrBr) complexes. The results show that the ring-shaped complexes are formed by a halogen bond (S···X) and a secondary hydrogen bond (H···X). We also analyzed the H2CS–ClF–ClF and FCl–H2CS–ClF complexes to investigate the cooperative and diminutive halogen bonding. The cooperative effect of halogen bonding is found in the former, while the diminutive effect is present in the latter. We finally considered the solvent effect on the halogen bond in H2CS–BrCl complex and found that the solvent has a prominent enhancing effect on it. The complexes have also been analyzed with natural bond orbital, atoms in molecules, and symmetry adapted perturbation theory method.
Effects of nitrogen doping on device characteristics of InSnO thin film transistor
Authors: Eun Kim Chang , Yun Ilgu
Published: January 2012

The effects of nitrogen doping on the performance of InSnO thin film transistor were investigated. When the nitrogen was doped in the InSnO channel, device characteristics such as turn-on voltage, subthreshold swing, field effect mobility, and on/off current ratio were enhanced. The N2 insertion in the deposition process decreased the density of the interface trap states and enhanced the crystallinity of the InSnO channel layer. These results indicate that device characteristics can be improved by nitrogen doping in the deposition process.
Temperature dependence of the thermal boundary resistivity of glass-embedded metal nanoparticles
Authors: Banfi Francesco , Juvé Vincent , Nardi Damiano , Dal Conte Stefano , Giannetti Claudio , Ferrini Gabriele , Del Fatti Natalia , Vallée Fabrice
Published: January 2012

The temperature dependence of the thermal boundary resistivity is investigated in glass-embedded Ag particles of radius 4.5 nm, in the temperature range from 300 to 70 K, using all-optical time-resolved nanocalorimetry. The present results provide a benchmark for theories aiming at explaining the thermal boundary resistivity at the interface between metal nanoparticles and their environment, a topic of great relevance when tailoring thermal energy delivery from nanoparticles as for applications in nanomedicine and thermal management at the nanoscale.
Passivation of InP heterojunction bipolar transistors by strain controlled plasma assisted electron beam evaporated hafnium oxide
Authors: Driad R. , Sah R. E. , Schmidt R. , Kirste L.
Published: January 2012

We present structural, stress, and electrical properties of plasma assisted e-beam evaporated hafnium dioxide (HfO2) layers on n-type InP substrates. These layers have subsequently been used for surface passivation of InGaAs/InP heterostructure bipolar transistors either alone or in combination with plasma enhanced chemical vapor deposited SiO2 layers. The use of stacked HfO2/SiO2 results in better interface quality with InGaAs/InP heterostructures, as illustrated by smaller leakage current and improved breakdown voltage. These improvements can be attributed to the reduced defect density and charge trapping at the dielectric-semiconductor interface. The deposition at room temperature makes these films suitable for sensitive devices.
Isotope effect in normal-to-local transition of acetylene bending modes
Authors: Ma Jianyi , Xu Dingguo , Guo Hua , Tyng Vivian , Kellman Michael E.
Published: January 2012

The normal-to-local transition for the bending modes of acetylene is considered a prelude to its isomerization to vinylidene. Here, such a transition in fully deuterated acetylene is investigated using a full-dimensional quantum model. It is found that the local benders emerge at much lower energies and bending quantum numbers than in the hydrogen isotopomer HCCH. This is accompanied by a transition to a second kind of bending mode called counter-rotator, again at lower energies and quantum numbers than in HCCH. These transitions are also investigated using bifurcation analysis of two empirical spectroscopic fitting Hamiltonians for pure bending modes, which helps to understand the origin of the transitions semiclassically as branchings or bifurcations out of the trans- and cis-normal bend modes when the latter become dynamically unstable. The results of the quantum model and the empirical bifurcation analysis are in very good agreement.
Accurate evaluation of interface state density in SiC metal-oxide-semiconductor structures using surface potential based on depletion capacitance
Authors: Yoshioka Hironori , Nakamura Takashi , Kimoto Tsunenobu
Published: January 2012

We propose a method to accurately determine the surface potential (ψS) based on depletion capacitance, and the interface state density (DIT) was evaluated based on the difference between quasi-static and theoretical capacitances in SiC metal-oxide-semiconductor capacitors (C−ψS method). We determined that this method gives accurate values for ψS and DIT. From the frequency dependence of the capacitance measured at up to 100 MHz, a significant fast-interface-state response exists at 1 MHz, which results in the overestimation of ψS if it is determined based on the flatband capacitance at 1 MHz. The overestimation of ψS directly affects the accuracy of the energy level. DIT at a specific energy level is underestimated by the overestimation of ψS. Furthermore, the fast interface states that respond at 1 MHz cannot be detected by the conventional high(1 MHz)-low method. The C−ψS method can accurately determine the interface state density including the fast states without high-frequency measurements.
The impact of awareness on epidemic spreading in networks
Authors: Wu Qingchu , Fu Xinchu , Small Michael , Xu Xin-Jian
Published: January 2012

We explore the impact of awareness on epidemic spreading through a population represented by a scale-free network. Using a network mean-field approach, a mathematical model for epidemic spreading with awareness reactions is proposed and analyzed. We focus on the role of three forms of awareness including local, global, and contact awareness. By theoretical analysis and simulation, we show that the global awareness cannot decrease the likelihood of an epidemic outbreak while both the local awareness and the contact awareness can. Also, the influence degree of the local awareness on disease dynamics is closely related with the contact awareness.
Nanoscale mechanically induced structural and electrical changes in Ge2Sb2Te5 films
Authors: Cecchini R. , Benítez J. J. , Sánchez-López J. C. , Fernández A.
Published: January 2012

We demonstrate that the microstructure and electrical properties of Ge2Sb2Te5 films can be changed by a nanoscale mechanical process. Nanoscratching is used to define modified areas onto an as-deposited crystalline Ge2Sb2Te5 film. Scanning tunneling microscopy measurements show that the modified areas have a very low electrical conductivity. Micro-Raman measurements indicate that the mechanically induced microstructural changes are consistent with a phase transformation from crystalline to amorphous, which can be reversed by laser irradiation.
Measurement of phase retardation of waveplate online based on laser feedback
Authors: Chen Wenxue , Li Haohao , Zhang Shulian , Long Xingwu
Published: January 2012

Polarization flipping accompanying with intensity transfer between two eigenstates of one laser mode happens when waveplate is placed in external cavity. The position of polarization flipping of two eigenstates is a function of phase retardation of waveplate. Phase retardation of waveplate is measured through analyzing the position of polarization flipping of two eigenstates. The measurement accuracy of phase retardation is 0.22°. A new structure of optical cement tray which can eliminate stress birefringence from optical cement process is invented. The accuracy of waveplate manufacture can be improved greatly based on the work of this article.
Theoretical study of the aqueous solvation of HgCl2: Monte Carlo simulations using second-order Moller-Plesset-derived flexible polarizable interaction potentials
Authors: Hernández-Cobos J. , Ramírez-Solís A. , Maron L. , Ortega-Blake I.
Published: January 2012

A study of the solvation of HgCl2 including ab initio aggregates of up to 24 water molecules and the results of extensive Monte Carlo simulations for the liquid phase using MP2-derived interaction potentials is presented. The interaction potentials are flexible, polarizable, and include non-additive effects. We conclude that a cluster description of the solvation mechanism is limited when compared to the condensed phase. The molecular image derived from the MC simulations is peculiar. It resembles that of a hydrophobic solute, which explains the rather easy passage of this neutral molecule through the cell membrane; however, it also shows an intermittent binding of one, two, or three water molecules to HgCl2 in the fashion of a hydrophilic solute.
Single lateral mode mid-infrared laser diode using wavelength-scale modulation of the facet reflectivity
Authors: Nash G. R. , Stokes J. L. , Pugh J. R. , Przeslak S. J. B. , Heard P. J. , Rarity J. G. , Cryan M. J.
Published: January 2012

The characteristics of mid-infrared laser diodes have been investigated before and after the patterning of wavelength-scale metallic apertures on the emitting facet. Before modification of the facet, the emitted spectrum consisted of a large number of peaks associated with different spatial modes, whereas afterwards, the spectrum was dominated by a single peak. Simulations showed that the patterning of the facet caused the effective reflectivity to be different for each lateral mode, suggesting that the peak in the measured spectra is associated with the single lateral mode which is most strongly reflected from the modified facet.
High field-gradient dysprosium tips for magnetic resonance force microscopy
Authors: Mamin H. J. , Rettner C. T. , Sherwood M. H. , Gao L. , Rugar D.
Published: January 2012

Magnetic resonance force microscopy (MRFM) is based on measuring the attonewton-scale force between nuclear or electronic spins and a magnetic tip. The force is directly proportional to the magnetic field gradient generated by the tip, making a high moment nanoscale magnet desirable. Dysprosium, with a bulk magnetization 70% higher than iron, is a suitable candidate for such a tip. We have performed MRFM to quantitatively characterize two Dy nanomagnets. We find that magnetic field gradients as high as 6 MT/m (60 G/nm) can be generated, a 40% enhancement compared to our previous FeCo tips.
Unsteady aspect of the electrohydrodynamic force produced by surface dielectric barrier discharge actuators
Authors: Debien A. , Benard N. , David L. , Moreau E.
Published: January 2012

The time-resolved electrohydrodynamic force produced by single dielectric barrier discharge (DBD) actuators used for airflow control is computed from electric wind velocity measurements. Two actuator designs are investigated: a plate-to-plate and a wire-to-plate surface DBD because each of them produces a different discharge current. Results show that: (1) the high voltage active electrode shape plays a key role in the plasma physics, (2) the body force is highly unsteady with fluctuations up to about ten times its time-averaged value, and (3) the typical plate-to-plate DBD produces a positive force during the positive half-cycle and a negative force during the negative half-cycle when both cycles result in a positive force with the wire-to-plate DBD.
Attenuation of extrinsic signaling reveals the importance of matrix remodeling on maintenance of embryonic stem cell self-renewal
Authors: Przybyla Laralynne M. , Voldman Joel
Published: January 2012

The role of extrinsic factors in maintaining self-renewal of embryonic stem cells (ESCs) has been extensively studied since the cells’ isolation, but the necessity for cell-secreted factors in self-renewal has remained undefined to date. Although it is generally accepted that addition of leukemia inhibitory factor (LIF) together with either serum or bone morphogenetic protein 4 (BMP4) is sufficient to maintain mouse ESCs (mESCs) in a self-renewing state, this does not preclude the possibility that autocrine factors are also required. Here we make use of a microfluidic perfusion device that is able to globally diminish diffusible autocrine signaling by applying continuous media flow to deplete cell-secreted factors. We demonstrate mESC culture for several days under continuous microfluidic perfusion and show that cell-secreted factors are removed and can be recovered downstream. We find that perturbing cell-secreted signaling causes mESCs to exit their stable self-renewing state in defined conditions that normally support self-renewal and to exhibit properties characteristic of epiblast cells. This state change is not due to the presence of the known autocrine differentiation inducer fibroblast growth factor 4, but, remarkably, it can be prevented by global remodeling of the extracellular matrix (ECM). We also find that cell-secreted matrix remodeling proteins are removed under perfusion and that inhibition of extracellular matrix remodeling causes mESCs to differentiate. Taken together, our data indicate that LIF and BMP4 are not sufficient to maintain self-renewal and that cell-secreted factors are necessary to continuously remodel the ECM and thereby prevent differentiation, revealing a previously undescribed level of mESC regulation through the use of microfluidic perfusion technology.
Lysine methyltransferase G9a methylates the transcription factor MyoD and regulates skeletal muscle differentiation
Authors: Ling Belinda Mei Tze , Bharathy Narendra , Chung Teng-Kai , Kok Wai Kay , Li SiDe , Tan Yong Hua , Rao Vinay Kumar , Gopinadhan Suma , Sartorelli Vittorio , Walsh Martin J. , Taneja Reshma
Published: January 2012

Skeletal muscle cells have served as a paradigm for understanding mechanisms leading to cellular differentiation. The proliferation and differentiation of muscle precursor cells require the concerted activity of myogenic regulatory factors including MyoD. In addition, chromatin modifiers mediate dynamic modifications of histone tails that are vital to reprogramming cells toward terminal differentiation. Here, we provide evidence for a unique dimension to epigenetic regulation of skeletal myogenesis. We demonstrate that the lysine methyltransferase G9a is dynamically expressed in myoblasts and impedes differentiation in a methyltransferase activity-dependent manner. In addition to mediating histone H3 lysine-9 di-methylation (H3K9me2) on MyoD target promoters, endogenous G9a interacts with MyoD in precursor cells and directly methylates it at lysine 104 (K104) to constrain its transcriptional activity. Mutation of K104 renders MyoD refractory to inhibition by G9a and enhances its myogenic activity. Interestingly, MyoD methylation is critical for G9a-mediated inhibition of myogenesis. These findings provide evidence of an unanticipated role for methyltransferases in cellular differentiation states by direct posttranslational modification of a transcription factor.
A quantum–quantum Metropolis algorithm
Authors: Yung Man-Hong , Aspuru-Guzik Alán
Published: January 2012

The classical Metropolis sampling method is a cornerstone of many statistical modeling applications that range from physics, chemistry, and biology to economics. This method is particularly suitable for sampling the thermal distributions of classical systems. The challenge of extending this method to the simulation of arbitrary quantum systems is that, in general, eigenstates of quantum Hamiltonians cannot be obtained efficiently with a classical computer. However, this challenge can be overcome by quantum computers. Here, we present a quantum algorithm which fully generalizes the classical Metropolis algorithm to the quantum domain. The meaning of quantum generalization is twofold: The proposed algorithm is not only applicable to both classical and quantum systems, but also offers a quantum speedup relative to the classical counterpart. Furthermore, unlike the classical method of quantum Monte Carlo, this quantum algorithm does not suffer from the negative-sign problem associated with fermionic systems. Applications of this algorithm include the study of low-temperature properties of quantum systems, such as the Hubbard model, and preparing the thermal states of sizable molecules to simulate, for example, chemical reactions at an arbitrary temperature.
Inhaled oxytocin amplifies both vicarious reinforcement and self reinforcement in rhesus macaques (
Macaca mulatta
)
Authors: Chang Steve W. C. , Barter Joseph W. , Ebitz R. Becket , Watson Karli K. , Platt Michael L.
Published: January 2012

People attend not only to their own experiences, but also to the experiences of those around them. Such social awareness profoundly influences human behavior by enabling observational learning, as well as by motivating cooperation, charity, empathy, and spite. Oxytocin (OT), a neurosecretory hormone synthesized by hypothalamic neurons in the mammalian brain, can enhance affiliation or boost exclusion in different species in distinct contexts, belying any simple mechanistic neural model. Here we show that inhaled OT penetrates the CNS and subsequently enhances the sensitivity of rhesus macaques to rewards occurring to others as well as themselves. Roughly 2 h after inhaling OT, monkeys increased the frequency of prosocial choices associated with reward to another monkey when the alternative was to reward no one. OT also increased attention to the recipient monkey as well as the time it took to render such a decision. In contrast, within the first 2 h following inhalation, OT increased selfish choices associated with delivery of reward to self over a reward to the other monkey, without affecting attention or decision latency. Despite the differences in species typical social behavior, exogenous, inhaled OT causally promotes social donation behavior in rhesus monkeys, as it does in more egalitarian and monogamous ones, like prairie voles and humans, when there is no perceived cost to self. These findings potentially implicate shared neural mechanisms.
Proapoptotic protein Bim is differentially required during thymic clonal deletion to ubiquitous versus tissue-restricted antigens
Authors: Suen Alexander Y. W. , Baldwin Troy A.
Published: January 2012

Positive and negative selection of thymocytes in the thymus are critical for the development of a mature and self-tolerant T-cell repertoire. The proapoptotic Bcl-2 family member Bim is important for negative selection by inducing apoptosis in thymocytes receiving a strong signal through their antigen receptor. However, in the case of ubiquitous self-antigens (UbA), Bim is not required for the clonal deletion of self-reactive thymocytes, suggesting the existence of nonapoptotic clonal deletion mechanisms. Unlike UbA, clonal deletion to tissue-restricted antigens (TRAs) requires positive selection and CCR7-mediated migration to the medulla. This led us to hypothesize that Bim is required for the latter. To study the role of Bim in clonal deletion to TRA, we constructed bone marrow (BM) chimeras using OT-I Bim-deficient or -sufficient donor bone marrow and recipients that express membrane bound chicken ovalbumin under control of the rat insulin promoter (Rip-mOVA). We found that clonal deletion to TRA was completely abrogated in the absence of Bim and large numbers of mature OT-I CD8 T cells survived in the periphery. Despite the large numbers of autoreactive T cells, the chimeras did not develop diabetes and OT-I Bim-deficient T cells from these chimeras were functionally impaired. Collectively, these data provide unique evidence of a differential, thymocyte-intrinsic, molecular requirement downstream of the T-cell receptor (TCR) for clonal deletion to UbA versus TRA and highlight the profound ability of other tolerance mechanisms to control T-cell autoreactivity in the absence of thymic clonal deletion.
Detecting anthrax in the mail by coherent Raman microspectroscopy
Authors: Arora Rajan , Petrov Georgi I. , Yakovlev Vladislav V. , Scully Marlan O.
Published: January 2012

In this report, we show the collection of spatial information through a turbid medium by coherent Raman microspectroscopic imaging. In particular, the technique is capable of identifying anthrax endospores inside a sealed paper envelope.
Atomically precise gold nanocrystal molecules with surface plasmon resonance
Authors: Qian Huifeng , Zhu Yan , Jin Rongchao
Published: January 2012

Since Faraday’s pioneering work on gold colloids, tremendous scientific research on plasmonic gold nanoparticles has been carried out, but no atomically precise Au nanocrystals have been achieved. This work reports the first example of gold nanocrystal molecules. Mass spectrometry analysis has determined its formula to be Au
333
(SR)
79
(R = CH
2
CH
2
Ph). This magic sized nanocrystal molecule exhibits fcc-crystallinity and surface plasmon resonance at approximately 520 nm, hence, a metallic nanomolecule. Simulations have revealed that atomic shell closing largely contributes to the particular robustness of Au
333
(SR)
79
, albeit the number of free electrons (i.e., 333 - 79 = 254) is also consistent with electron shell closing based on calculations using a confined free electron model. Guided by the atomic shell closing growth mode, we have also found the next larger size of extraordinarily stability to be Au
∼530
(SR)
∼100
after a size-focusing selection—which selects the robust size available in the starting polydisperse nanoparticles. This work clearly demonstrates that atomically precise nanocrystal molecules are achievable and that the factor of atomic shell closing contributes to their extraordinary stability compared to other sizes. Overall, this work opens up new opportunities for investigating many fundamental issues of nanocrystals, such as the formation of metallic state, and will have potential impact on condensed matter physics, nanochemistry, and catalysis as well.
Time-dependent magnetization in epitaxial hard magnetic thin films
Authors: Collocott S J , Neu V
Published: January 2012

Time-dependent magnetic behaviour at room temperature is investigated in highly oriented epitaxial hard magnetic thin films. Single-layer films with nominal composition PrCo5 and PrCo7 were studied, along with two SmCo5/Fe/SmCo5 trilayer films, with Fe layer thicknesses of 11 and 16 nm. The films were prepared using pulsed laser deposition on Cr buffered MgO (110) substrates. For the trilayer system, judicious choice of the thickness of the hard (SmCo5) and soft (Fe) magnetic layers results in an exchange-coupled two-phase magnet. All the thin films exhibit switching behaviour, i.e. a near square hysteresis loop, and the details of this behaviour are explored through both measurement of the hysteresis loop, at very slow field sweep rates, and the irreversible susceptibility, χirr. Measurements of the sweep rate dependence of the intrinsic coercivity, and magnetic viscosity on the major hysteresis loop were performed. For each film, three techniques were used to determine the fluctuation field, H
f: from the sweep rate data; from the magnetization relaxation data using the waiting time method; and from S/χirr, where S is the magnetic viscosity coefficient. Differences in the value of H
f determined using the three different techniques, and the equivalence of the three techniques, are discussed. Further insights into the time-dependent behaviour of the magnetization are gained from observations of the spontaneous remagnetization, following dc demagnetization. The study shows the thin films to be of high-stability. Furthermore, it supports the view that magnetization reversal in these materials is most likely an incoherent process, and not a process involving the uniform reversal of a grain. The model of weak pinning provides a useful framework for understanding magnetization processes.
Reasonableness and its definition in the provision of health care
Authors: Daniels Norman
Published: January 2012

Two central goals of health policy are to improve population health as much as possible and to distribute the improvements fairly. These goals will often conflict. Reasonable people will disagree about how to resolve these conflicts, which take the form of various unsolved rationing problems. The conflict is also illustrated by the ethical controversy that surrounds the use of cost-effectiveness analysis. Because there is no consensus on principles to resolve these disputes, a fair process is needed to assure outcomes that are perceived to be fair and reasonable. One such process, accountability for reasonableness, assures transparency, involves stakeholders in deliberating about relevant rationales, and requires that decisions be revised in light of new evidence and arguments. It has been influential in various contexts including developed countries such as Canada, the United Kingdom, New Zealand, and Sweden, and developing countries, such as Mexico....
Sustaining innovation in an era of specialized medicine
Authors: Termeer Henri A.
Published: January 2012

We are living in an era of unprecedented biomedical innovation. In recent years, new therapies have improved the prognosis of numerous intractable disorders that were previously neglected—in some cases changing diseases from a death sentence to a manageable chronic condition.

Our increased understanding of the genetic basis of disease will continue to fuel the creation of innovative therapies for many decades. Many of even the most enterprising therapies being introduced today are only a bridge to the definitive cures that gene therapy, stem cells, and other advances may offer....
Stroke: cerebrovascular disease
Authors: van Gijn J
Published: January 2012

Case History—Four cases of headache.

Cerebrovascular diseases include many pathological conditions but the principal categories are (1) infarction—through occlusion of major arteries, small arteries or venous sinuses; and (2) haemorrhage—most often through rupture of small arteries, arterial aneurysms or capillaries.

Strokes are common, with annual incidence rates for subjects aged over 55 ranging from 420 to over 1000 per 100 000. They are the most important case of disability in developed Western nations and the second most frequent cause of death after coronary heart disease. About 80% of strokes are caused by cerebral infarcts, with the remainder due to haemorrhage, with 20% of these attributable to a bleeding cerebral aneurysm. The incidence of transient ischaemic attacks (TIAs) is about 50 per 100 000....
Idiopathic intracranial hypertension
Authors: Lawton N.F.
Published: January 2012

Case History—A 40 yr old man presenting with headache and visual disturbance.

Idiopathic intracranial hypertension is a syndrome of raised intracranial pressure in the absence of an intracranial mass lesion, enlargement of the cerebral ventricles due to hydrocephalus, or venous thrombosis in the dural sinuses. Impaired cerebrospinal fluid absorption and raised cerebral venous pressure have both been implicated. Obese females of childbearing age are predominantly affected. Rarely, provocative factors include tetracycline, vitamin A derivatives, hypervitaminosis A, and vitamin A excess....
Global burden of disease: causes, levels, and intervention strategies
Authors: Laxminarayan Ramanan , Jamison Dean
Published: January 2012

Recent decades have seen remarkable progress in quantifying the burden of disease in low- and middle-income countries and in gathering evidence on the effectiveness and cost-effectiveness of health interventions. This chapter reviews the major sources of death and disability in these countries and draws lessons from recent analytical work on the cost-effectiveness of interventions to address this disease burden. Four essential messages emerge:...
The cost of health care in Western countries
Authors: White Joseph
Published: January 2012

All advanced industrial countries socialize most health care costs because their citizens view relatively equal access to such care as a mark of a decent society. This makes the costs of health care a policy issue, because governments need to relate costs to revenues, and there are limits to the willingness of citizens, especially wealthier citizens, to pay for others....
A sinister pathogen corrupts two disciplines: the demographic entrapment of Middle Africa
Authors: King Maurice
Published: January 2012

Are starvation and violence ‘diseases’? If they are, a textbook of medicine must be prepared to recognize some novel pathogens. The most sinister cause of these two diseases is ‘demographic entrapment’, which occurs when a subsistence community exceeds (1) the carrying capacity of its local ecosystem (too many people for the land to support), (2) its ability to migrate to new land, and (3) the ability of its economy to produce goods and services, which it can exchange for food and other essentials. The outcome of entrapment is severe poverty, starvation and violence, and the problem is at its worst in Middle Africa, where populations multiplied seven times during the 20th century, and are expected to triple again by 2050. Remedy will not be found unless fertility is reduced, if necessary to one child only per family, but discussion of this is prevented by powerful taboos....
Intracellular signalling
Authors: Floto R. Andres
Published: January 2012

This section outlines the general principles of intracellular signalling. Focusing on cell surface receptors, the requirements for effective transmission of information across the plasma membrane are outlined. The principal mechanisms utilized in mammalian signal transduction are described. For each, the pathological consequences of aberrant signalling and means by which pathways can be pharmacologically targeted are described in molecular terms....
Discovery of embryonic stem cells and the concept of regenerative medicine
Authors: Evans Martin J.
Published: January 2012

In this chapter Sir Martin Evans, who was awarded the Nobel Prize for Physiology or Medicine in 2007, describes the identification of stem cells, initially from certain cultured tumour cells (teratocarcinoma cells) and latterly from early mammalian embryos.

The differentiated cells of the adult vertebrate arise from a single fertilized egg and as development proceeds the commitment to differentiation becomes irreversible....
Allergy
Authors: Ewan Pamela
Published: January 2012

Allergy is common and becoming commoner: it now affects about one-third of the United Kingdom population. This is being driven by environmental changes, which are also leading to an increase in both the complexity and severity of the condition. In addition to the traditional allergic disorders—asthma, rhinitis, and eczema—multisystem allergic disease and reactivity to several allergens are now common; new allergies have appeared, including those due to foods, drugs, and diagnostic agents; and anaphylaxis is increasing....
The nature and development of cancer
Authors: Benson John R. , Liau Siong-Seng
Published: January 2012

Contemporary ideas of carcinogenesis envisage a series of random genetic changes that confer a selective growth advantage over healthy cells. These changes collectively lead to the disruption of coordinated networks of intercellular communication and cause a fundamental change in cellular behaviour which affects processes such as proliferation, differentiation, and apoptosis. This progressive dysregulation of cellular function implies that cancer is not a morphological entity, but a process in which the malignant phenotype is gradually acquired....
Epidemiology of sexually transmitted infections
Authors: Mabey David
Published: January 2012

Although accurate incidence figures are not available in most countries, sexually transmitted infections (STIs) (excluding HIV) are estimated to cause more than 5% of the global burden of disease. The burden falls especially heavily on women and infants, with more than half a million perinatal deaths attributable to syphilis annually. Mobile populations, those with many sexual partners, and those whose partners have many partners are at increased risk, and the prevalence of treatable STIs is many times higher in poor populations, who often lack access to effective treatment. Other STIs, especially those that cause genital ulceration, increase the risk of HIV transmission....
Pelvic inflammatory disease
Authors: Eschenbach David
Published: January 2012

Pelvic inflammatory disease (PID) is an infection of the fallopian tubes caused by a wide variety of bacteria, including Chlamydia trachomatis, Neisseria gonorrhoeae, and genital tract bacteria, most notably anaerobes.

Manifestations of PID range from mild pelvic pain and tenderness to severe peritonitis. Pelvic abscess formation is a serious infectious complication. However, only about 40% of patients with PID have a fever and even fewer have severe infectious manifestations. Thus, PID is often not diagnosed and it is commonly confused with other pelvic conditions, with a differential diagnosis that most notably includes ectopic pregnancy, appendicitis, and ovarian cyst....
Injuries, envenoming, poisoning, and allergic reactions caused by animals
Authors: Warrell David A.
Published: January 2012

Attacks by wild and domesticated animals are increasing worldwide. They are best prevented by taking local advice. Injuries usually occur in places remote from medical care and may involve extensive trauma, haemorrhagic shock, and a high risk of bacterial contamination. First aid is resuscitation, control of bleeding and perforating injuries, intravenous fluid replacement, and rapid evacuation to hospital for emergency surgery and treatment of infection....
Bioterrorism
Authors: Green Manfred S.
Published: January 2012

Bioterrorism is the deliberate use of biological agents to cause illness, death and fear for ideological or personal purposes. Most potential bioterrorism agents occur naturally as known pathogens and are classified as follows: (1) Category A, with greatest risk to the public and national security, comprising (a) infectious and contagious diseases, smallpox, plague, and viral haemorrhagic fevers; (b) infectious but not contagious diseases, anthrax, and tularaemia; and ...
Cold
Authors: Stroud M.A.
Published: January 2012

Humans are poorly adapted to cold, which can cause hypothermia, nonfreezing cold injury, and frostbite.

This occurs especially with wind and wetting, and is seen indoors in older people and those who are thin. At a core temperature of 35 °C, victims complain of cold, act appropriately, shiver, and are peripherally vasoconstricted, but with further cooling they may become confused or drowsy and appropriate physiological responses disappear. Coma occurs at 26 to 32 °C, and death typically at 17 to 26 °C. General investigation and management is as for any comatose patient, but specific issues include (1) accurate measurement of core temperature requires a low-reading rectal thermometer; (2) measurement of serum amylase (risk of pancreatitis) and creatine kinase (risk of rhabdomyolysis); (3) rewarming—if onset of cooling was prolonged, rewarming should generally be slow; (4) diagnosis of death—apparently dead victims should be rewarmed whenever possible before resuscitation is abandoned....
Drowning
Authors: Fenner Peter J.
Published: January 2012

Drowning is a major preventable cause of death, most frequently in children and in developing countries. Aspiration (whether of salt or fresh water) is usual in drowning and near-drowning (known as non-fatal, or submersion injury) and leads to cardiac arrest within a few minutes. Death or severe neurological impairment occurs after submersion for more than 5 to 10 min, but much longer durations may be tolerated in hypothermic conditions....
Lightning and electrical injuries
Authors: Andrews Chris
Published: January 2012

Lightning strikes are rare accidents but carry a 10% case fatality, killing 0.1 to 0.3 per million population each year. During thunderstorms, the risk is increased by sheltering under trees or by being on open water, on tractors, or in open fields or golf courses....
Principles of clinical pharmacology and drug therapy
Authors: O’Shaughnessy Kevin
Published: January 2012

The role of clinical pharmacology is to provide the scientific basis for rational prescribing: ‘patients may recover in spite of drugs … or because of them’ (Gaddum). This sums up the dilemma facing any doctor who prescribes a drug to a patient: it should certainly be the doctor’s explicit intention to do the patient some good, but the drug may actually harm the patient, and on rare occasions it can even kill them....
Severe malnutrition
Authors: Jackson Alan A.
Published: January 2012

Severe malnutrition is the consequence of systemic deficiency of energy and nutrients over a prolonged period: in children development is stunted and the individual is at risk of fatal (often clinically ‘silent’) infection and other illnesses. It is a medical and societal emergency: mortality is high, despite attempts to provide appropriate care....
Disorders of purine and pyrimidine metabolism
Authors: Watts Richard W.E.
Published: January 2012

These disorders are due to abnormalities in the biosynthesis, interconversion and degradation of the purines—adenine and guanine—and of the pyrimidines—cytosine, thymine and uracil. All are heterocyclic bases which exist in tri-, di-, and mono-phosphorylated forms, and as either deoxyribosylated or ribosylated derivatives (deoxyribose and ribose are pentose carbohydrates). The phosphorylated deoxyribosylated and ribosylated derivatives are termed ‘nucleotides’, and the purely ribosylated derivatives, which lack the phosphate group, are ‘nucleosides’....
Breast cancer
Authors: Cariati M. , Holmberg L. , Mansi J. , Parker P. , Pichert G. , Pinder S. , Sawyer E. , Wilson R. , Purushotham A.
Published: January 2012

Epidemiology and aetiology—over 1 million women worldwide are diagnosed with breast cancer each year, with about 400 000 dying of the disease. Familial breast cancer, most commonly related to the BRCA1 and BRCA2 genes, accounts for only 5% of all cases. Many of the known risk factors are not modifiable because they are inherent or would require unrealistic lifestyle changes, but moderating alcohol consumption, avoiding obesity, and increasing physical activity are all possibly useful interventions....
Benign breast disease
Authors: Clarke P. Jane , Fiddes R.
Published: January 2012

Benign conditions of the breast are very common, but they cause great anxiety, often leading the patient to be concerned that she has breast cancer. Symptoms may include: (1) a mass in the breast, commonly due to fibroadenoma, benign cystic change, or macrocysts; (2) mastalgia; and (3) discharge from the nipple, which may be caused by hyperprolactinaemia, intraduct papilloma, or duct ectasia. Management involves exclusion of malignancy, often by triple assessment of any palpable abnormality (for clinical examination, radiological and pathological assessment, see ...
Normal growth and its disorders
Authors: Butler Gary
Published: January 2012

Normal growth has three phases: rapid in infancy and adolescence, steady during mid childhood. Height should always be interpreted within the context of the family: short or tall stature is often familial; idiopathic short stature occurs when the height of a normal child is below their target range....
Puberty
Authors: Banerjee I. , Clayton P.E.
Published: January 2012

Puberty is characterized by well-defined physical changes as a child moves from the prepubertal state through the stages of puberty to full sexual development. The outward signs usually develop over 3 to 5 years, with significant variation both in the age that puberty starts and the pace at which development proceeds....
Hormonal manifestations of nonendocrine disease
Authors: Barber T.M. , Wass John A.H.
Published: January 2012

Tumours (usually but not invariably malignant), other ‘nonendocrine conditions’ and drugs can be associated with a wide variety of endocrine syndromes. ‘Ectopic’ hormone secretion, defined as the release of a hormone from a site different from the gland that normally produces it, has classically been recognized in the context of neoplasia, but it is now apparent that many hormones are synthesized by ‘nonendocrine’ tissue. Although a particular endocrinopathy may be associated with a specific type of tumour in a particular organ, the relationship is not invariable, and many neoplasms elaborate more than one hormonal substance at the same or at different times and thus produce a mixed endocrine picture....
Medical management of normal pregnancy
Authors: Williams David J.
Published: January 2012

Reducing the number of maternal deaths is one of the United Nation’s eight Millennium Development Goals, yet despite this initiative maternal deaths are increasing in some parts of Africa, usually from readily preventable causes that would not occur in the presence of a skilled birth attendant....
Renal disease in pregnancy
Authors: Firth John D.
Published: January 2012

Urinary tract infection—2 to 10% of pregnancies are complicated by asymptomatic bacteriuria, which progresses to symptomatic infection in 40% of cases and is associated with adverse fetal outcome. Antibiotic treatment reduces the chances of developing symptomatic infection and of infants being born with low birth weight....
Structure and function of the gut
Authors: Thompson D.G.
Published: January 2012

The gastrointestinal tract is a hollow tube stretching from the oral cavity through the oesophagus, stomach, small intestine, colon, and rectum to the anal sphincter. Its function is the transport, digestion, and elimination of ingested material to supply nutrients, vitamins, minerals, and electrolytes that are essential for life, together with the protection of the rest of the body from injurious or allergenic material. The stomach acts as a storage, sterilizing, and digestive tank; the small intestine is the major site of digestion and absorption; the colon’s function is to salvage water and electrolyte from the small intestinal effluent; and the rectum provides a storage function, enabling the elimination of colonic residue (defecation) to be restricted to times of personal convenience....