bluuebunny/crossref_metadata_2025 huggingface dataset:
Schizophrenia and violence
Authors: Matthias  , Angermeyer C.
Published: May 2005

Objective: The relationship between schizophrenia and violence is studied from a psychiatric and a public health perspective.

Method: All epidemiological studies which have been published since 1990 are reviewed.

Results: Despite differences in the methodological approaches chosen the studies reviewed concur in supporting the assumption that there is a moderate but significant association between schizophrenia (or more generally psychotic disorders) and violence. However, compared with the magnitude of risk associated with substance abuse and personality disorders, that associated with schizophrenia or other major mental disorders is small. In addition, the elevated risk to behave violently appears to be limited to particular symptom constellations. The evidence available so far suggests that the proportion of violent crimes committed by people suffering from a severe mental disorder is small. There is no unambiguous evidence of an increase of violent acts committed by severely mentally ill people in general and people suffering from schizophrenia in particular during recent years. Strangers appear to be at an even lower risk of being violently attacked by someone suffering from severe mental disorder than by someone who is mentally healthy.

Conclusion: While the assessment of relative risk is of great interest for psychiatric researchers who are trying to identify factors which may increase or decrease the risk of violent behaviour among the mentally ill, which in turn may provide some clues as to how to intervene best in order to reduce the risk, the attributable risk is of special interest for the public since it informs about the risk of becoming victim of a violent act committed by someone who is suffering from a mental disorder.
Family work for schizophrenia: practical application
Authors: Leff Julian
Published: May 2005

Objective: To review the evidence for the efficacy, efficiency and effectiveness of family work for schizophrenia.

Method: The review is based on the relevant literature but is not intended to be exhaustive, except in the area of practical application.

Results: The effectiveness of family work has been established by a series of randomized controlled trials. Relatives groups are efficient in terms of staff time, and multiple family groups may be more efficacious than sessions with single families. However, a substantial proportion of relatives refuse to attend a group and need sessions in the home. Family work skills can be acquired by clinicians working in ordinary settings, although few studies have addressed this question. Problems have been encountered regularly by trained community workers trying to practise their newly acquired skills.

Conclusion: Difficulties in implementation may be remedied by adopting a systemic approach and including the managers of the service in the initial training sessions.
Psychological therapy in schizophrenia: what is the evidence?
Authors: Brenner H. D.
Published: May 2005

Objective: The present contribution provides a critical outline of the current position of psychological therapies in schizophrenia.

Method: Therefore, empirical research into the efficacy of psychological interventions in the treatment of schizophrenic disorders has been reviewed.

Results: Four cognitive‐behavioural approaches have emerged as pre‐eminently effective, or at least especially promising, as adjuncts to pharmacotherapy, i.e. the training of social skills, cognitive training programs for the remediation of neurocognitive deficits, psychoeducative, coping‐orientated interventions with patients and their families, and cognitive‐behavioural therapy of residual symptoms. These approaches are discussed with regard to their efficacy in reducing relapse rates, psychopathology as well as cognitive and social disability.

Conclusion: Open questions and possibilities for the further development of these approaches are considered and prognostications are made concerning the future of psychotherapy research in schizophrenia, notably in the light of changing conditions in public health care systems.
Compliance with antipsychotic treatment
Authors: Oehl M. , Hummer M. , Fleischhacker W. W.
Published: May 2005

Objective: Despite the demonstrated efficacy of antipsychotics the relapse rate among patients with schizophrenia remains high. One major reason for this is non‐compliance. In this article we review different factors influencing compliance and discuss possibilities to enhance compliance among schizophrenic patients.

Method: This review is based on a systematic literature search in Medline.

Results: We summarize the four main factors (patient‐, environment‐, physician‐ and treatment‐related) that influence compliance and discuss possible measures to enhance compliance. Next to many other variables discussed in more detail, it is crucial to ensure a positive doctor–patient relationship and to provide sufficient information about the benefit/risk ratio of the medication as well as about the illness itself to build up and sustain compliance. Significant others should be included into the therapeutic alliance whenever possible.

Conclusion: Despite many published reports on compliance, it remains to be a problem of eminent clinical relevance. Clinicians must not underestimate it in order to optimize the treatment of patients with schizophrenia.
Integrating pharmacological and psychosocial treatments for schizophrenia
Authors: Stephen  , Marder R.
Published: May 2005

Objective: The objective of this study was to develop principles of combining pharmacological and psychosocial treatment that can be useful for clinicians who are treating patients with schizophrenia.

Method: Research studies in schizophrenia that controlled both pharmacological and psychosocial treatments were reviewed. These included studies using conventional and newer antipsychotics as well as a number of psychosocial methods.

Results: The interactions between the forms of treatment appear to be more than merely additive, since each can enhance the effects of the other. Drug and psychosocial treatments may affect different outcome domains, with the former affecting symptoms and the later affecting social outcomes. Recent studies using newer antipsychotics suggest that these agents improve the participation of patients in psychosocial treatments.

Conclusion: Understanding the interactions between psychosocial and pharmacological treatments can be useful for clinicians who are developing treatment strategies for patients with schizophrenia. Newer agents with different side‐effect profiles and broader effectiveness appear to have improved the outcomes of psychosocial treatments.
Actigraphy to measure day structure as a therapeutic variable in the treatment of schizophrenic patients
Authors: Haug Hans‐Joachim , Wirz‐Justice Anna , Rössler Wulf
Published: May 2005

Objective: A component of social skills is the ability to adapt to the social rhythms of the environment. Patients with schizophrenia are often disabled in this adaptation. Thus, structuring activities throughout the day has long been known as part of psychosocial treatments. Actigraphy as a tool to measure acitvity and circadian rhythms may even serve as an indicator for the day‐structuring of schizophrenic patients.

Method: Actigraphy was used in a patient with affective disorder and one with chronic schizophrenia for more than 2 weeks.

Results: In comparison to a regular 24‐hour rest–activity cycle in a depressed patient, the actigraph of the patient with schizophrenia presents active phases at night, irregular activity levels at day and signs of a delayed‐sleep‐phase syndrome.

Conclusion: Actigraphy could serve as a tool to investigate activity levels and circadian rest–activity phases, even in schizophrenia. There may be some further benefit of actigraphy as a tool in psychosocial treatments.
The schizophrenic patient in the somatic hospital
Authors: Munk‐Jørgensen P. , Mors O. , Mortensen P. B. , Ewald H.
Published: May 2005

Objective: There is an increased risk in schizophrenia for premature death from illnesses in almost all organic systems. The present study analyses the Rate Ratio (RR) for schizophrenic patients' admissions to somatic departments in Denmark.

Method: 20 000 schizophrenic patients were identified in the Danish Psychiatric Central Register and 200 000 sex‐ and age‐matched controls were identified in the Danish Central Person Register. Both groups were searched for in the Danish National Patient Register in which admissions to all somatic departments are registered. Pulmonary and cardiovascular diseases are used as examples.

Results: RR is increased for several diseases, especially infectious, up to a maximum of RR=4.15 for severe heart failures and decreased to as low as RR=0.35 for atherosclerotic diseases of the brain vessels.

Conclusion: It seems that individuals with schizophrenia are rarely treated for their physical illness in its early, less severe phases, but more likely in its acute phases when the disease is severe, life‐threatening or painful.
Delayed Treatment with Monoclonal Antibody IN-1 1 Week after Stroke Results in Recovery of Function and Corticorubral Plasticity in Adult Rats
Authors: Seymour Andrew B , Andrews Ellen M , Tsai Shih-Yen , Markus Tiffanie M , Bollnow Melanie R , Brenneman Miranda M , O'Brien Timothy E , Castro Anthony J , Schwab Martin E , Kartje Gwendolyn L
Published: May 2005

Neuronal death due to ischemic stroke results in permanent deficits in sensory, language, and motor functions. The growth-restrictive environment of the adult central nervous system (CNS) is an obstacle to functional recovery after stroke and other CNS injuries. In this regard, Nogo-A is a potent neurite growth-inhibitory protein known to restrict neuronal plasticity in adults. Previously, we have found that treatment with monoclonal antibody (mAb) IN-1 to neutralize Nogo-A immediately after stroke enhanced motor cortico-efferent plasticity and recovery of skilled forelimb function in rats. However, immediate treatment for stroke is often not clinically feasible. Thus, the present study was undertaken to determine whether cortico-efferent plasticity and functional recovery would occur if treatment with mAb IN-1 was delayed 1 week after stroke. Adult rats were trained on a forelimb-reaching task, and the middle cerebral artery was occluded to induce focal cerebral ischemia to the forelimb sensorimotor cortex. After 1 week, animals received mAb IN-1 treatment, control antibody, or no treatment, and were tested for 9 more weeks. To assess cortico-efferent plasticity, the sensorimotor cortex opposite the stroke lesion was injected with an anterograde neuroanatomical tracer. Behavioral analysis demonstrated a recovery of skilled forelimb function, and anatomical studies revealed neuroplasticity at the level of the red nucleus in animals treated with mAb IN-1, thus demonstrating the efficacy of this treatment even if administered 1 week after stroke.
Model for the elastic behavior near intermartensitic transitions
Authors: Dai Liyang , Cullen James , Wuttig Manfred
Published: May 2005

Transitions between different martensitic states have been observed in Ni0.50Mn0.284Ga0.216 using elastic constant measurements. In this paper, we develop a model to explain the reentrant behavior based on a Landau expansion of the free energy in strain space. Here, we assume that the coefficient of the third-order term as well as the second-order term has significant temperature dependence. This assumption results in a C′ versus temperature in good agreement with observation. The model and possible modifications to it are discussed and compared to the elastic constant data.
Controlling the exchange interaction using the spin-flip transition of antiferromagnetic spins in Ni81Fe19∕α-Fe2O3
Authors: Dho Joonghoe , Leung C. W. , Barber Z. H. , Blamire M. G.
Published: May 2005

We have studied exchange bias and coercivity in ferromagnetic (FM) Ni81Fe19 layers coupled with antiferromagnetic (AF) (0001), (112¯0), and (11¯02) α-Fe2O3 layers. We show that the exchange interaction between FM and AF layers is controllable by a magnetic-field annealing (MFA) through a spin reorientation temperature of an AF material, similar to a MFA through a Nèel temperature in normal exchange-biased systems. For (112¯0) and (11¯02) α-Fe2O3, the temperature-dependent exchange bias displayed a sudden increase below a spin-flip temperature of α-Fe2O3 (Tm) and the coercivity showed a clear variation near Tm.
Effect of W underlayer on the crystal orientation and microstructure of NdFeB thin films
Authors: Liu Xiaoxi , Okumoto Takaaki , Matsumoto Mitsunori , Morisako Akimitsu
Published: May 2005

The effects of W underlayer on the crystal orientation and microstructure of NdFeB thin films were studied. NdFeB films with excellent perpendicular orientation could be grown on W underlayer with (110) orientation. It is found that the magnetic properties of NdFeB films depended sensitively on the underlayer thickness. This is attributed to the grainsize, surface roughness, crystal orientation, and the ability of resistance to Nd oxidation of the W underlayer.
Magnetocaloric effect in itinerant electron metamagnetic systems La(Fe1−xCox)11.9Si1.1
Authors: Hu F. X. , Gao J. , Qian X. L. , Ilyn Max , Tishin A. M. , Sun J. R. , Shen B. G.
Published: May 2005

The NaZn13-type compounds La(Fe1−xCox)11.9Si1.1 (x=0.04, 0.06, 0.08) were successfully synthesized, in which the Si content is the limit that can be reached by arc-melting technique. TC is tunable from 243 to 301 K with Co doping from x=0.04 to 0.08. Great magnetic entropy change ΔS in a wide temperature range from ∼230 to ∼320K has been observed. The adiabatic temperature change ΔTad upon changing magnetic field was also directly measured. ΔTad of sample x=0.06 reaches ∼2.4K upon a field change from 0 to 1.1 T. The temperature hysteresis upon phase transition is small, ∼1K, for all samples. The influence of Co doping on itinerant electron metamagnetic transition and magnetic entropy change is discussed.
Exchange-bias phenomena and modeling in nanocrystalline powders of MnO/FeCo and NiO/Fe
Authors: Cornejo D. R. , Padrón Hernández E. , Azevedo A. , Rezende S. M.
Published: May 2005

An approach towards the modeling of the magnetic behavior in heterogeneous systems of exchange-coupled antiferromagnetic (AF) and ferromagnetic (FM) particles with composition (AF)x+(FM)1−x is presented. The model is based on the Preisach hysteresis model and correctly predicts the correlation between the exchange-bias field and the mean grain size of the material, as established from the measurements of the hysteresis loops in mechanically alloyed (MnO)+(α−FeCo). The model was also used to calculate the unidirectional anisotropy interface energies in both this and (NiO)x+(α−Fe)1−x system; in the latter case, the predicted value was in full agreement with that reported for antiferromagnetic layers of NiO.
Probing the local magnetization reversal through magnetoresistance measurement
Authors: Lo I. C. , Wu J. C. , Horng Lance , Wei Zung-Hang , Lai Mei-Fang , Chang C. R.
Published: May 2005

A microstructured permalloy ellipse with six equally spaced nonmagnetic voltage leads has been studied through magnetoresistance measurements and magnetic force microscopy. The aspect ratio and film thickness of the element having three vortices of magnetic configuration were accordingly designed and fabricated using electron-beam lithography through a lift off process. Magnetoresistance curves measured with various pairs of voltage leads have revealed a local magnetic-moment reversal. Two magnetoresistance kinks observed with decreasing∕increasing field strength can be attributed to the vortex formation∕annihilation, which was confirmed by magnetic force microscopy and micromagnetic simulation. The motion of the vortex core driven by the transverse external magnetic field was estimated to be 4.1 nm∕Oe.
Interface roughness effects on coercivity and exchange bias
Authors: Dantas Ana L. , Rebouças G. O. G. , Silva A. S. W. T. , Carriço A. S.
Published: May 2005

We report model calculations of the hysteresis loops of exchange-coupled ferromagnet/antiferromagnet bilayers with monolayer-scale roughness and show that the loops are affected by the combined effect of the interface field strength, the degree of magnetic roughness and magnetostatic effects. The magnetization reversal may occur via domain-wall nucleation at the edges of monoatomic interface steps or coherent magnetization rotation. A magnetic phase diagram is constructed for a 10-nm-thick Fe film, subjected to nanometer-scale interface roughness.
Magnetic and transport measurements on the layered III-VI diluted magnetic semiconductor In1−xMnxSe
Authors: Pekarek T. M. , Arenas D. J. , Miotkowski I. , Ramdas A. K.
Published: May 2005

Magnetic and transport properties of single-crystalline In1−xMnxSe (x=0.01 and 0.10) have been measured. In1−xMnxSe exhibits a prominent magnetization hysteresis between 90 and 290K. In1−xMnxSe is conducting with increasing resistance at low temperatures and a small hysteresis between 90 and 290K with the cooling trace having lower resistivity. The magnetization above and below the hysteresis is consistent with a paramagnetic signal. A Curie–Weiss fit to the data yields a value of Jeff∕kB=−240K. The data are consistent with a saturated component contributing to the hysteresis and a paramagnetic phase that scales with concentration.
Magnetic properties of BaM∕Pd–Pt double-layered thin film deposited at various substrate temperatures
Authors: Nahar Shams Nazmun , Liu Xiaoxi , Matsumoto Mitsunori , Morisako Akimitsu
Published: May 2005

Crystallographic and magnetic properties of barium ferrite (BaM) thin films deposited onto Pt, Pd, and an alloy of Pd–Pt underlayers by sputtering at different substrate temperatures (Ts) from 400to600°C have been studied. It is found that the coercivity values in the perpendicular direction (Hcperp) of the BaM∕Pd–Pt films are higher than those of the BaM films deposited on Pd and Pt underlayers. C-axis orientation of BaM∕Pd–Pt film can be achieved at very low Ts of 450°C with a Hcperp of 2.1kOe for 30-nm BaM.
The possible origin of large magnetic anisotropy of Fe3Pt alloy thin films
Authors: Nahid M. A. I. , Suzuki Takao
Published: May 2005

The magnetic anisotropy of Fe3Pt alloy thin films and its origin are studied. The maximum magnetic anisotropy constants K1 and K2 of Fe3Pt thin films grown onto MgO(100) and MgO(111) substrates are determined to be about −4×106 and 2×107erg∕cc at room temperature. A close relationship exists between the magnetic anisotropy constants and structural parameter. The magnetic anisotropy constants of Fe3Pt alloy thin films may originate from the magnetocrystalline anisotropy and also possibly due to pair ordering.
Structure and magnetic properties of mechanically alloyed Tb0.7Pr0.3(Fe0.9B0.1)1.93 and the magnetostriction of its epoxy composites
Authors: Liu J. J. , Ren W. J. , Zhao X. G. , Liu W. , Zhang Z. D.
Published: May 2005

The C15 Laves phase with composition Tb0.7Pr0.3(Fe0.9B0.1)1.93 has been synthesized by mechanical alloying and subsequent annealing process. The structure and magnetic properties of Tb0.7Pr0.3(Fe0.9B0.1)1.93 have been investigated. The effect of the annealing on the magnetic properties has been studied. The samples annealed at 773K are found to have a coercivity of 6.66kOe at room temperature. The coercivity decreases monotonically with increase in the annealing temperature. The epoxy∕Tb0.7Pr0.3(Fe0.9B0.1)1.93 composites have been produced by a cold compression-molding technique. The magnetostriction of the epoxy∕Tb0.7Pr0.3(Fe0.9B0.1)1.93 composites with different weight ratios of epoxy resin to powder is measured by a standard strain technique. The Tb0.7Pr0.3(Fe0.9B0.1)1.93 composites, with a weight ratio of epoxy resin to powder of 5:100, have a high magnetostriction of 810ppm, at an applied magnetic field of 12kOe. The Tb0.7Pr0.3(Fe0.9B0.1)1.93 alloy combines a high magnetostriction with a low coercivity, which is a promising magnetostrictive material.
Magnetic normal modes of nanoelements
Authors: McMichael R. D. , Stiles M. D.
Published: May 2005

Micromagnetic calculations are used to determine the eigenfrequencies and precession patterns of some of the lowest-frequency magnetic normal modes of submicron patterned elements. Two examples are presented. For a Permalloy-like ellipse, 350nm×160nm×5nm thick in zero field, the lowest frequency normal mode at 4GHz corresponds to precession in the “ends” of the ellipse. Other resonant frequencies are compared with the frequencies of spinwaves with discrete wave vectors. For a normally magnetized 50nmdiameter×15nm thick cobalt disk, the calculated eigenfrequencies increase linearly with applied field, mimicking the behavior of the experimental critical current for spin transfer instabilities in an experimental realization of this disk.
Cluster-assembled exchange-spring nanocomposite permanent magnets
Authors: Rui X. , Sun Z. G. , Xu Y. , Sellmyer D. J. , Shield J. E.
Published: May 2005

Isotropic nanocomposite magnetic structures were produced via cluster assembly routes with energy products reaching 18 MG Oe. Gas aggregation produces Fe clusters with an average size less than 10 nm with a very narrow size distribution, and these were embedded in a hard magnetic matrix by cosputtering of FePt. Structures produced were crystallographically isotropic with Fe cluster phase content ranging from 0 to 30 vol %. The coercivity decreased from 13 kOe as Fe cluster content increased. Single-phase-type hysteresis loops indicating excellent exchange coupling at low Fe cluster content give way to a stepped demagnetization loop at an Fe cluster content greater than 20%. The energy product initially increased with Fe cluster content, then decreased.
Effect of contact geometry on the magnetoresistance response of Ni80Fe20 antidot array
Authors: Wang C. C. , Adeyeye A. O. , Wu Y. H.
Published: May 2005

The effect of electrical contact geometry on the shape and sign of the magnetoresistance (MR) response in micron-size antirectangular array structures has been investigated. The MR response is strongly sensitive to the direction of the applied sense current. The results can be attributed to the competing anisotropic MR effects from two inhomogeneous orthogonal current flows in the structure. We have also investigated the effect of film thickness on the overall MR responses, and observed that as film thickness decreases, the switching field and MR ratio decrease accordingly and the competition between the anisotropic MR effects becomes more evident.
Magnetic and electrical-transport property variations of epitaxially grown MnAs thin films
Authors: Song J. H. , Lee J. J. , Cui Y. , Ketterson J. B.
Published: May 2005

We have studied the magnetic and electrical-transport property variations of epitaxial MnAs thin films grown on Si(001) and GaAs(001) substrates by molecular beam epitaxy as a function of the growth temperature and film thickness. All samples show a ferromagnetic behavior with the exception of MnAs∕Si(001) deposited at low growth temperatures. Interestingly, the electrical-transport properties change from metallic to semiconducting on decreasing the total thickness from 300to20nm for MnAs∕GaAs(001) samples. These results indicate a radical change of the electronic structure of the MnAs layer.
Valve behavior of giant magnetoimpedance in field-annealed Co70Fe5Si15Nb2.2Cu0.8B7 amorphous ribbon
Authors: Phan Manh-Huong , Peng Hua-Xin , Wisnom Michael R. , Yu Seong-Cho , Chau Nguyen
Published: May 2005

The influence of longitudinal field annealing on the giant magnetoimpedance (GMI) effect in Co70Fe5Si15Nb2.2Cu0.8B7 amorphous ribbons has been investigated. It was found that annealing in the open air at magnetic fields smaller than the anisotropy field along the ribbon gave rise to the GMI-valve phenomenon, while annealing at magnetic fields higher than the anisotropy field significantly reduced the GMI effect. The GMI-valve behavior corresponding to the highest field sensitivity of GMI (125%∕Oe) was observed at a frequency of 0.1 MHz in the ribbon annealed under an applied field of 2 Oe. This is ideal for developing sensitive and quick-response magnetic sensors. The GMI-valve behavior observed in the Co-based amorphous ribbon due to field annealing can be explained by considering the complex permeability spectra in relation to the rotational dc magnetization.
Structural and magnetic properties of epitaxial ferromagnetic-antiferromagnetic manganite multilayers
Authors: Morán O. , Gomez M. E. , Ramirez J. G. , Schwarz T. , Fuchs D. , Hott R. , Schneider R.
Published: May 2005

We have studied the exchange bias (EB) interaction in ferromagnetic La2∕3Ca1∕3MnO3∕antiferromagnetic La1∕3Ca2∕3MnO3 superlattices fabricated on single crystal (001)-(LaAlO3)0.3(Sr2AlTaO6)0.7 (LSAT) substrates using pulsed laser deposition. The as-grown multilayers were characterized with respect to their magnetic and structural properties by means of dc superconducting quantum interference device magnetometry and x-ray diffraction (XRD) measurements, respectively. The field cooling loop is shifted towards negative fields compared to the zero-field cooling measurement, indicating an EB effect. The XRD profile with clearly resolved superlattice Bragg peaks and multiple satellite peaks around (00l) Bragg reflections of the LSAT substrate gives evidence of a well defined superlattice structure.
High-bandwidth terahertz radiation from ponderomotively accelerated carriers using Bessel–Gauss femtosecond pulses
Authors: Chau K. J. , Dechant A. L. , Elezzabi A. Y.
Published: May 2005

Terahertz generation from high intensity excitation of a semiconductor plasma by a radially polarized Bessel–Gauss femtosecond pulse is modeled. The results are compared with Gaussian pulses of equivalent fluence. Due to carrier confinement, a radially polarized Bessel–Gauss pulse exerts a significantly stronger ponderomotive force on photocarriers than a Gaussian pulse, resulting in an order of magnitude increase in the THz emission power.
Large displacement of germanium atoms in crystalline Ge2Sb2Te5
Authors: Shamoto S. , Yamada N. , Matsunaga T. , Proffen Th. , Richardson J. W. , Chung J.-H. , Egami T.
Published: May 2005

Local structure of NaCl-type crystalline Ge2Sb2Te5 has been studied by the atomic pair distribution function analysis of pulsed neutron powder diffraction data. We have found the large displacement of germanium atoms in this crystalline phase. Usually, such a large lattice distortion has disadvantages for the electric conductivity. The electronic band structure, however, implies that this significant distortion in addition to the lattice defect at Na site reduces only thermal conductivity, while the highly ordered tellurium atoms at Cl site keep high electric conductivity.
Vortex-chirality control in mesoscopic disk magnets observed by photoelectron emission microscopy
Authors: Taniuchi T. , Oshima M. , Akinaga H. , Ono K.
Published: May 2005

We demonstrate the vortex-chirality control in mesoscopic disk magnets using photoelectron emission microscopy (PEEM). Micrometer-sized vortex-chirality-control devices of permalloy were designed and fabricated by electron-beam lithography and lift-off. The magnetic images were obtained by PEEM using the x-ray magnetic circular dichroism (XMCD) with circularly polarized synchrotron radiation. The XMCD-PEEM observation reveals that the vortex chirality in the designed devices was perfectly controlled by an external applied magnetic field.
Large electrostrictive strain at gigahertz frequencies in a polymer nanoactuator: Computational device design
Authors: Strachan Alejandro , Goddard William A.
Published: May 2005

Using molecular dynamics with a first-principles-based force field (denoted MSXX), we show that large electrostrictive strains (∼5%) at extremely high frequencies (over ∼109Hz) can be achieved in a poly(vinylidene-fluoride) nanoactuator if the packing density of the polymer chains is chosen appropriately. We control the packing density by assembling the polymer chains on a silicon ⟨111⟩ surface with one-half coverage. Under these conditions, the equilibrium, zero electric field conformation of the polymer contains a combination of gauche and trans bonds. This structure can be transformed to an all-T conformation by applying an external electric field. Such molecular transformation is accompanied by a large deformation in the direction of the polymer chains. The device shows typical electrostrictive behavior with strain proportional to the square of the polarization.
Bias voltage effect on tunnel magnetoresistance in fully epitaxial MgO double-barrier magnetic tunnel junctions
Authors: Nozaki T. , Hirohata A. , Tezuka N. , Sugimoto S. , Inomata K.
Published: May 2005

Double-barrier magnetic tunnel junctions (DMTJs), consisting of a fully epitaxial Fe(001)∕MgO(001)∕Fe(001)∕MgO(001)∕Fe(001) structure, have been deposited onto MgO (001) single-crystal substrates using molecular-beam epitaxy, and have been characterized by measuring the bias voltage effects on both tunneling magnetoresistance (TMR) and conductance. The DMTJs are found to show large TMR ratios of up to 110% and extremely small bias voltage dependence(Vhalf=1.44V under a positive bias application) compared with conventional magnetic tunnel junctions (MTJs) with a single MgO barrier at room temperature. In addition, clear asymmetry is observed in the bias voltage dependence of the TMR ratios with respect to the signs of the bias, which corresponds to the asymmetric bias dependence of the conductance, especially for a parallel magnetization configuration. Such a high Vhalf with a large TMR ratio is relevant for a high-output MTJ cell for future spintronic devices.
Dynamic spectral interferometry for measuring the nonlinear amplitude and phase response of a saturable absorber mirror
Authors: Stibenz Gero , Steinmeyer Günter , Richter Wolfgang
Published: May 2005

We report on spectral interferometry for measuring the spectrally resolved nonlinear phase and amplitude response in a pump–probe experiment. Using nJ pulses from a femtosecond oscillator, we demonstrate the method by measuring the nonlinear response of a GaAs∕AlGaAs single-quantum-well saturable absorber mirror. The demonstrated sub-mrad phase sensitivity constitutes a two-order-of-magnitude improvement of phase resolution, compared to earlier demonstrations. Dynamic spectral interferometry proves to be a powerful tool for evaluating the phase response on nonlinear optical semiconductor devices for mode locking of lasers, optical switching, and other photonic applications.
Origin of ferromagnetism in Fe- and Cu-codoped ZnO
Authors: Shim Jeong Hyun , Hwang Taesoon , Lee Soonchil , Park Jung Hye , Han Seung-Jin , Jeong Y. H.
Published: May 2005

Fe- and Cu-codoped ZnO was previously reported as a room-temperature dilute magnetic semiconductor. We have investigated the origin of the ferromagnetism in Zn0.95−xFe0.05CuxO using the zero-field Fe57 nuclear magnetic resonance and neutron diffraction. These measurements reveal that some Fe ions of Zn0.95−xFe0.05CuxO form a secondary phase, ZnFe2O4. Detailed comparison of nuclear magnetic resonance spectra of Zn0.95−xFe0.05CuxO, bulk ZnFe2O4 with normal spinel structure, and nanocrystalline ZnFe2O4 with inverted spinel structure shows that the secondary phase possesses an inverted spinel structure and is ferrimagnetic at room temperature, while normal zinc ferrite is nonmagnetic. The ferromagnetism in Fe- and Cu-codoped ZnO stems from the secondary phase, while the majority of Fe ions substituted into the ZnO lattice appears to remain magnetically inert.
Snapthrough occurring in the postbuckling of thin films
Authors: Parry G. , Colin J. , Coupeau C. , Foucher F. , Cimetière A. , Grilhé J.
Published: May 2005

The postbuckling transition from an initially straight-sided wrinkle to a distribution of bubbles has been investigated by means of finite element simulations in the case of a thin film relying on a rigid substrate. The calculations show that a snapthrough occurs when the buckling wavelength exceeds a critical value. Experimental atomic force microscopy observations of this transition have been reported and found to be in good agreement with the calculations.
GaN-based photocathodes with extremely high quantum efficiency
Authors: Uchiyama Shoichi , Takagi Yasufumi , Niigaki Minoru , Kan Hirofumi , Kondoh Haruyasu
Published: May 2005

We have fabricated phototubes with photocathodes consisting of the Mg-doped GaN films. The spectral shapes of the response and the quantum efficiency (QE) strongly depend on the Mg-doping concentration. The calibrated QE of the photocathode is maximized to be 71.9% at a photon energy of 5.4 eV by a Mg-doping concentration of 3.0×1019cm−3. Consequently, a phototube with the GaN-based photocathode is realized to demonstrate a very high QE, more than 50% and sharp cutoff characteristic over three orders of magnitude.
Microwave operation and modulation of a transistor laser
Authors: Chan R. , Feng M. , Holonyak N. , Walter G.
Published: May 2005

The microwave operation and modulation (3GHz) of an InGaP∕GaAs heterojunction bipolar transistor (HBT) laser is reported. The HBT layer structure is in the form of an optical waveguide (with cleaved ends) that also includes an InGaAs recombination quantum well in the p-type base region to improve the recombination radiation properties. The shift in HBT laser operation from spontaneous to stimulated emission is manifest as a distinct change in the HBT current–voltage characteristics, specifically a decrease in the common-emitter current gain (βdc=IC∕IB) and the occurrence of even a more striking peak in the small signal (ac) gain βac=ΔIC∕ΔIB.
Increase of the thermoelectric power factor in Cu∕Bi∕Cu,Ni∕Bi∕Ni, and Cu∕Bi∕Ni composite materials
Authors: Odahara Hirotaka , Yamashita Osamu , Satou Kouji , Tomiyoshi Shoichi , Tani Jun-ichi , Kido Hiroyasu
Published: May 2005

The resultant thermoelectric power factors P of three types of Cu∕Bi∕Cu,Ni∕Bi∕Ni, and Cu∕Bi∕Ni composite materials welded with Bi were measured at 298 K as a function of relative thickness of Bi and compared with P values calculated by treating these devices as an electrical and thermal circuit. It was first demonstrated experimentally that the observed P values of composite devices have a local maximum at an optimum volume fraction (corresponding to the thickness) of Bi, as predicted theoretically. The maximum P values of composite materials were several times higher than those of pure Ni and Bi and were about 100 times larger than that of pure Cu. The dependence of P on the thickness of Bi was found to be explained roughly by introducing the modified thermal conductivity and an enhancement factor in the Seebeck coefficient to our simple model in which a device was treated as an electrical and thermal circuit.
A Monte Carlo study of amphiphilic dendrimers: Spontaneous asymmetry and dendron separation
Authors: Giupponi G. , Buzza D. M. A.
Published: May 2005

We study via Monte Carlo simulation the conformation of amphiphilic dendrimers for which terminal monomers (t) and internal monomers (i) interact differently with the solvent (s). Specifically, we have studied g=3,6 dendrimers as a function of χit, χis, and χts (χ is the differential contact energy between the different particles) for parameter values χit=0,±1 and −1<χis, χts<1. We have allowed negative χ values in order to model attractive polar interactions (e.g., hydrogen bonding) which are believed to be important in many dendrimer/solvent systems. We find the “phase diagram” of dendrimer conformations to be extremely rich and to be a strong function of g, χis, and χts but only a weak function of χit. For χis, χts>0, we observe dendrimer conformations, such as unimolecular normal micelles and inverted loopy micelles. However, for χis<0 or χts<0, we observe more exotic molecular conformations, for example, the spontaneous development of asymmetry and dendron separation. These properties are analyzed in terms of snapshots as well as more quantitatively in terms of the radii of gyration, radial density profiles, pair-correlation functions, degree of asymmetry, and dendron overlap factor. By exploiting the dramatic conformational changes under different solvent conditions, we suggest the possibility of using amphiphilic dendrimers as stimuli-responsive smart materials.
Rate of homogeneous crystal nucleation in molten NaCl
Authors: Valeriani C. , Sanz E. , Frenkel D.
Published: May 2005

We report a numerical simulation of the rate of crystal nucleation of sodium chloride from its melt at moderate supercooling. In this regime nucleation is too slow to be studied with “brute force” molecular-dynamics simulations. The melting temperature of (“Tosi Fumi”) NaCl is ∼1060K. We studied crystal nucleation at T=800 and 825K. We observe that the critical nucleus formed during the nucleation process has the crystal structure of bulk NaCl. Interestingly, the critical nucleus is clearly faceted, the nuclei have a cubical shape. We have computed the crystal-nucleation rate using two completely different approaches, one based on an estimate of the rate of diffusive crossing of the nucleation barrier, the other based on the forward flux sampling and transition interface sampling methods. We find that the two methods yield the same result within an order of magnitude. However, when we compare the extrapolated simulation data with the only available experimental results for NaCl nucleation, we observe a discrepancy of nearly five orders of magnitude. We discuss the possible causes for this discrepancy.
Moving waves and spatiotemporal patterns due to weak thermal effects in models of catalytic oxidation
Authors: Nekhamkina Olga , Sheintuch Moshe
Published: May 2005

We analyze the behavior of a microkinetic model of a catalytic reaction coupled with weak enthalpy effects to show that under fixed gas-phase concentrations it can produce moving waves with an intrinsic length scale, when the underlying kinetics is oscillatory. The kinetic model incorporates dissociative oxygen adsorption, reactant adsorption and desorption, and surface reaction. Three typical patterns may emerge in a one-dimensional system (a long wire or a ring): homogeneous oscillations, a family of moving waves propagating with constant velocities, and patterns with multiple source∕sink points. Pattern selection depends on the ratio of the system length to the intrinsic wave length and the governing parameters. We complement these analysis with simulations that revealed a plethora of patterned states on one- and two-dimensional systems (a disk or a cylinder). This work shows that weak long-range coupling due to high feed rates maintains such patterns, while low feed rates or strong long-range interaction can gradually suppress the emerging patterns.
Micropatterning of metal substrate by adhesive force lithography
Authors: Seo Soon-min , Park Jeong-yong , Lee Hong H.
Published: May 2005

We introduce adhesive force lithography (AFL), a detachment-based method for patterning metal surface. In this method, all the polymer layer except for the desired pattern gets lifted up from the metal surface. The craze microstructure unique to thin polymer films on the order of 102nm is utilized for this AFL along with a difference in adhesive force at two interfaces. Poly(urethaneacrylate) mold, which has a high enough work of adhesion with polymer, makes AFL effective. This technique is purely additive, fast (∼10s contact time), and applicable to large area patterning (10cm×10cm).
Recoil anisotropy following multiphoton dissociation via near-resonant intermediate states
Authors: Dixon Richard N.
Published: May 2005

Expressions are derived for the moments βn of the anisotropy of fragment recoil following multiphoton dissociation. The results for all possible two- and three-photon excitation pathways from a Σ or Π initial state, with prompt dissociation, are listed in tabular and graphical form, thereby facilitating the identification of pathways compatible with experimental data. The consequence of possible interference between multiple-excitation pathways is discussed. In addition, allowance is made for rotation of the parent molecule in the dissociating state on the time scale of its dissociation, with specific equations for three cases: fully resolved rotation on excitation, significant but unresolved rotation, and the intermediate case of partially resolved excitation. Finally, expressions are given for the consequence of significant rotation in a near-resonant intermediate state. It is pointed out that the effects of rotation can lead to a strong variation of the anisotropic moments over an excitation band, and that the absence of rotational features does not necessarily imply that the effects of rotation on recoil anisotropy can be ignored. The application of the theory is illustrated for a number of model systems, restricted to diatomic molecules with possible rotation but subsequent axial recoil. However, the expressions are easily adapted to polyatomic systems, provided that any fragment rotation is unresolved.
Stark and field-born resonances of an open square well in a static external electric field
Authors: Emmanouilidou Agapi , Moiseyev Nimrod
Published: May 2005

The resonance positions, widths (inverse lifetimes), and wave functions of a square-potential well in the presence of a static electric field are calculated by using the outgoing boundary conditions. Our study concentrates on the field-born states that, unlike the well-known Stark resonances, are not associated with the field-free bound states. The effect of a lower cutoff of the static field on the field-born resonance phenomena is studied. The feasibility of experiments, where the isolated long-lived and overlapping short-lived field-born resonances can be explored, is discussed.
Impact of growth conditions on vacancy-type defects in silicon–germanium structures grown by molecular-beam epitaxy
Authors: Shoukri Kareem M. , Haddara Yaser M. , Knights A. P. , Coleman P. G.
Published: May 2005

Silicon–germanium layers of either 200nm or 250nm have been grown via molecular-beam epitaxy (MBE) on p-type (001) silicon substrates. Each sample was prepared using a unique combination of buffer-layer type, buffer-layer growth temperature, and layer Ge content. Vacancy-type defects have been identified using beam-based positron annihilation. These results, combined with those from previous work, indicate the size and concentration of defects in MBE grown SiGe layers depend strongly upon the buffer-layer growth temperature (T). For T>500°C vacancy point defect concentrations are below the detectable limit of the measurement. As T is decreased to 300°C, vacancy clusters form in the buffer layer and point defects appear in the SiGe film, even for a SiGe growth temperature of 500°C.
Stretching globular polymers. I. Single chains
Authors: Craig A. , Terentjev E. M.
Published: May 2005

We review the force-extension behavior of polymers collapsed in poor solvent, modified to include the effects of semiflexibility and considered for globules with “ordered” and “disordered” internal structures. A series of ordered globules is used as a model for the unbinding of a disordered globule beneath its glass transition and for multiple-repeat proteins such as the poly-Ig-domain titin used in atomic force microscopy studies. These single-chain results form the foundation for the treatment of cross-linked networks of globular polymers.
Resonantly diode laser pumped 1.6-μm-erbium-doped yttrium aluminum garnet solid-state laser
Authors: Garbuzov Dmitri , Kudryashov Igor , Dubinskii Mark
Published: May 2005

We report direct resonant diode pumping of a 1.6-μm-Er3+-doped bulk solid-state laser. Using a 1470-nm-single-mode diode laser module to pump the Er:YAG rod, an absorbed photon conversion efficiency of 26% has been obtained in this initial experiment. Analysis of the diode-pumped solid-state laser input–output characteristics suggests that the obtained slope efficiency can be doubled through the reduction of intracavity losses and pumping efficiency improvement.
Harmonic generation from chromium plasma
Authors: Ganeev R. A. , Suzuki M. , Baba M. , Kuroda H.
Published: May 2005

The generation of up to the 33rd harmonic (λ=24.12nm) of a Ti:sapphire laser pulse using prepulse-produced chromium plasma as a nonlinear medium was demonstrated. A steep decrease of intensity for low-order harmonics (up to the 15th order) was followed by a plateau. A considerable restriction of 27th harmonic generation was observed in different focusing conditions.
Light absorption enhancement by nanoparticles
Authors: Sukmanowski J. , Viguié J.-R. , Nölting B. , Royer F. X.
Published: May 2005

Multilayer optical resonance systems containing nanoparticles of aluminium (Al), silver (Ag), and nickel (Ni) placed on a layer of SiO2, which itself was coated on an Al mirror with submicrometer thickness, were analyzed regarding their absorption of light. Atomic force microscopy images of the distributions of the metallic nanoparticles in the manufactured layers are presented. Reflection measurements carried out under different conditions show that nanoparticle layers of only a few nanometers average thickness can significantly affect light absorption if spatial distribution and size of the particles are suitably chosen. Reasons for this effect of an enhanced absorption compared with classical absorbers and potential applications of such layers with nanoparticles are discussed.
Reynolds number effects in the outer layer of the turbulent flow in a channel with rough walls
Authors: Bakken Ole Martin , Krogstad Per-Åge , Ashrafian Alireza , Andersson Helge I.
Published: May 2005

Turbulent channel flow measurements for two different rough surfaces have been compared with a smooth reference case. A range of Reynolds numbers, Reτ∊⟨360,6000⟩, has been investigated using hot-wire anemometry. Reynolds stresses and third-order moments are shown to be very little affected by the substantially different wall conditions outside 5k, where k is the characteristic length scale of the roughness. In this region, a reasonably good collapse with Reynolds number is demonstrated when scaling with friction velocity is used. This contrasts some of the rough-wall investigations previously published for boundary layers and channels with only one rough wall. It is believed that the differences observed are due to the differences in boundary conditions and that symmetrically roughened channel flows and flows in rough-wall pipes may be better candidates for the Townsend’s wall similarity hypothesis than asymmetrical flows.
Cantilever surface stress sensors with single-crystalline silicon piezoresistors
Authors: Rasmussen P. A. , Hansen O. , Boisen A.
Published: May 2005

We present a cantilever with piezoresistive readout optimized for measuring the static deflection due to isotropic surface stress on the surface of the cantilever [Sens. Actuators B 79(2–3), 115 (2001)]. To our knowledge nobody has addressed the difference in physical regimes, and its influence on cantilever sensors with integrated piezoresistive readout, that one finds between typical atomic force microscopy measurements and the surface stress sensors used in, e.g., biochemical measurements. We have simulated the response from piezoresistive cantilevers as a function of resistor type and placement for the two different regimes, i.e., surface stress measurements and force measurements. The model thus provides the means to specifically design piezoresistive cantilevers for surface stress measurements.
Step control of vicinal 6H–SiC(0001) surface by H2 etching
Authors: Nakajima A. , Yokoya H. , Furukawa Y. , Yonezu H.
Published: May 2005

Anisotropic step bunching on vicinal 6H–SiC(0001) surface induced by H2 etching was investigated. Step structures were observed using atomic force microscopy and high-resolution transmission electron microscopy at off angle <2°. The etched surfaces exhibited three types of step bunching: (1) straight six-bilayer steps, (2) straight six-bilayer steps and nanofacets, and (3) zigzag three-bilayer steps. The step height and density can be controlled by a tilt angle and direction of a vicinal surface. Mechanisms of the step bunching processes are discussed at points of an anisotropy of lateral-etching rates and surface-free energies.