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1.
Phys Rev Lett ; 113(23): 236602, 2014 Dec 05.
Article in English | MEDLINE | ID: mdl-25526144

ABSTRACT

We report on spin injection into a high mobility 2D electron system confined at an (Al,Ga)As/GaAs interface, using (Ga,Mn)As Esaki diode contacts as spin aligners. We measured a clear nonlocal spin valve signal, which varies nonmonotonically with the applied bias voltage. The magnitude of the signal cannot be described by the standard spin drift-diffusion model, because at maximum this would require the spin polarization of the injected current to be much larger than 100%, which is unphysical. A strong correlation of the spin signal with contact width and electron mean free path suggests that ballistic transport in the 2D region below ferromagnetic contacts should be taken into account to fully describe the results.

2.
Phys Rev Lett ; 111(9): 097201, 2013 Aug 30.
Article in English | MEDLINE | ID: mdl-24033065

ABSTRACT

We report high-resolution hard x-ray photoemission spectroscopy results on (Ga,Mn)As films as a function of Mn doping. Supported by theoretical calculations we identify, for both low (1%) and high (13%) Mn doping values, the electronic character of the states near the top of the valence band. Magnetization and temperature-dependent core-level photoemission spectra reveal how the delocalized character of the Mn states enables the bulk ferromagnetic properties of (Ga,Mn)As.

3.
J Theor Biol ; 336: 144-57, 2013 Nov 07.
Article in English | MEDLINE | ID: mdl-23899941

ABSTRACT

We investigate the evolution of bet-hedging in a population that experiences a stochastically switching environment by means of adaptive dynamics. The aim is to extend known results to the situation at hand, and to deepen the understanding of the range of validity of these results. We find three different types of evolutionarily stable strategies (ESSs) depending on the frequency at which the environment changes: for a rapid change, a monomorphic phenotype adapted to the mean environment; for an intermediate range, a bimorphic bet-hedging phenotype; for slowly changing environments, a monomorphic phenotype adapted to the current environment. While the last result is only obtained by means of heuristic arguments and simulations, the first two results are based on the analysis of Lyapunov exponents for stochastically switching systems.


Subject(s)
Environment , Models, Biological , Stochastic Processes , Computer Simulation , Phenotype , Population Density
4.
Nat Commun ; 4: 2068, 2013.
Article in English | MEDLINE | ID: mdl-23820766

ABSTRACT

Spin injection and extraction are at the core of semiconductor spintronics. Electrical injection is one method of choice for the creation of a sizeable spin polarization in a semiconductor, requiring especially tailored tunnel or Schottky barriers. Alternatively, optical orientation can be used to generate spins in semiconductors with significant spin-orbit interaction, if optical selection rules are obeyed, typically by using circularly polarized light at a well-defined wavelength. Here we introduce a novel concept for spin injection/extraction that combines the principle of a solar cell with the creation of spin accumulation. We demonstrate that efficient optical spin injection can be achieved with unpolarized light by illuminating a p-n junction where the p-type region consists of a ferromagnet. The discovered mechanism opens the window for the optical generation of a sizeable spin accumulation also in semiconductors without direct band gap such as Si or Ge.

5.
Nanotechnology ; 23(46): 465202, 2012 Nov 23.
Article in English | MEDLINE | ID: mdl-23092817

ABSTRACT

We have grown an ultrathin epitaxial Fe/MgO bilayer on (Ga, Mn)As by e-beam evaporation in UHV. The system structure has been investigated by high resolution transmission electron microscopy (TEM) experiments which show that the Fe and MgO films, covering completely the (Ga, Mn)As, grow with the epitaxial relationship Fe[100](001) [parallel] MgO[110](001) [parallel] (Ga,Mn)As[110](001). The magnetic reversal process, studied by the magneto-optical Kerr effect (MOKE) at room temperature, demonstrates that the iron is ferromagnetic and possesses a cubic anisotropy, confirming the epitaxy relationship found with TEM. Resistivity measurements across the barrier display a non-Ohmic behavior characterized by cubic conductance as a function of the applied voltage suggesting tunneling-dominated transport across the barrier.

6.
J Med Eng Technol ; 36(3): 156-62, 2012 Apr.
Article in English | MEDLINE | ID: mdl-22316101

ABSTRACT

A microfluidic pressure sensor with inductively coupled, wireless readout capability has been developed for integration into cerebrospinal fluid shunt valve implants. The sensor consists of a deformable PDMS film that is bonded over a microfluidic reservoir, forming a fluidic capacitor. Deflection of the capacitor membrane is detected remotely through a shift in the resonance frequency of a micro-fabricated LC circuit. Sensors were fabricated by a combination of conventional MEMS technologies and rapid soft lithography. A direct pattern transfer technique was used to pattern the deformable PDMS film with a metal coating for the capacitive readout. The mechanical response of the fluidic capacitor was characterized by measuring the deflection of the PDMS film using an extrinsic Fabry-Perot interferometer (EFPI), and wireless sensing was demonstrated by the shift in resonance frequency of the sensor via an inductively coupled antenna. The sensor transduces pressure into a change in resonant frequency with sensitivity > 3.4 ppm Pa⁻¹ and responsivity 4.6 kHz Pa⁻¹, over a dynamic range of 0~3 kPa.


Subject(s)
Cerebrospinal Fluid Shunts/methods , Micro-Electrical-Mechanical Systems/instrumentation , Microfluidic Analytical Techniques/instrumentation , Monitoring, Physiologic/instrumentation , Monitoring, Physiologic/methods , Dimethylpolysiloxanes , Equipment Design , Pressure , Transducers, Pressure , Wireless Technology/instrumentation
7.
J Med Eng Technol ; 36(3): 169-73, 2012 Apr.
Article in English | MEDLINE | ID: mdl-22339111

ABSTRACT

We have designed, built and tested a novel device for placing intradural neurmodulator implants directly on the pial surface of the spinal cord. This applier tool is designed for ergonomic handling of delicate electro-mechanical devices such as the Iowa-Patch™ spinal cord stimulator implant, which is aimed at overcoming certain shortcomings in the performance of standard epidural stimulator devices. The applier is approximately 14 cm long, 6 mm in diameter, made of stainless steel components, and has simple and reliable mechanisms for the attachment and release of the implant from it. We describe the design of the device, details of its construction, and its performance during in vivo testing of somatosensory evoked potentials in an ovine model of intradural spinal cord stimulation.


Subject(s)
Dura Mater/surgery , Neural Prostheses , Neurosurgical Procedures/instrumentation , Spinal Cord/surgery , Animals , Equipment Design , Humans , Male , Models, Biological , Sheep
8.
J Med Eng Technol ; 36(1): 22-5, 2012 Jan.
Article in English | MEDLINE | ID: mdl-22188575

ABSTRACT

We have designed, built and tested a novel spinal cord surrogate that mimics the low-amplitude cardiac-driven pulsations of the human spinal cord, for use in developing intradural implants to be used in a novel form of neuromodulation for the treatment of intractable pain and motor system dysfunction. The silicone surrogate has an oval cross section, 10 mm major axis × 6 mm minor axis, and incorporates a 3 mm diameter × 3 cm long angioplasty balloon that serves as the pulsation actuator. When pneumatically driven at 1 Hz and 1.5 atmospheres (≈ 1140 mm Hg), the surrogate's diametric pulsation is ≈ 100 µm, which corresponds well to in vivo observations. The applications for this surrogate are presented and discussed.


Subject(s)
Electric Stimulation Therapy/instrumentation , Spinal Cord/physiology , Electrodes, Implanted , Equipment Design , Pain, Intractable/therapy
9.
Phys Rev Lett ; 107(18): 187203, 2011 Oct 28.
Article in English | MEDLINE | ID: mdl-22107669

ABSTRACT

We report x-ray photoemission spectroscopy results on (Ga,Mn)As films as a function of both temperature and Mn doping. Analysis of Mn 2p core level spectra reveals the presence of a distinct electronic screening channel in the bulk, hitherto undetected in more surface sensitive analysis. Comparison with model calculations identifies the character of the Mn 3d electronic states and clarifies the role, and the difference between surface and bulk, of hybridization in mediating the ferromagnetic coupling in (Ga,Mn)As.

10.
Phys Rev Lett ; 107(5): 056601, 2011 Jul 29.
Article in English | MEDLINE | ID: mdl-21867085

ABSTRACT

We investigate the increase of the Curie temperature T(C) in a lateral spin injection geometry where the ferromagnetic (Ga,Mn)As injector and detector contacts are capped by a thin iron film. Because of interlayer coupling between Fe and (Ga,Mn)As T(C) gets enhanced by nearly 100% for the thinnest (Ga,Mn)As films. The use of the proximity effect might pave the way for practical implementation of spintronic devices.

11.
Article in English | MEDLINE | ID: mdl-21086207

ABSTRACT

A dynamic model was developed to simulate complex interactions of mechanical stability, revascularisation and tissue differentiation in secondary fracture healing. Unlike previous models, blood perfusion was included as a spatio-temporal state variable to simulate the revascularisation process. A 2D, axisymmetrical finite element model described fracture callus mechanics. Fuzzy logic rules described the following biological processes: angiogenesis, intramembranous ossification, chondrogenesis, cartilage calcification and endochondral ossification, all of which depended on local strain state and local blood perfusion. In order to evaluate how the predicted revascularisation depended on the mechanical environment, we simulated two different healing cases according to two groups of transverse metatarsal osteotomies in sheep with different axial stability. The model predicted slower revascularisation and delayed bony bridging for the less stable case, which corresponded well to the experimental observations. A revascularisation sensitivity analysis demonstrated the potential of the model to account for different conditions regarding the blood supply.


Subject(s)
Fracture Healing , Models, Biological , Neovascularization, Physiologic , Fuzzy Logic , Humans , Stress, Mechanical
12.
Phys Rev Lett ; 103(8): 087203, 2009 Aug 21.
Article in English | MEDLINE | ID: mdl-19792755

ABSTRACT

We report on electrical measurements of the effective density of states in the ferromagnetic semiconductor material (Ga,Mn)As. By analyzing the conductivity correction to an enhanced electron-electron interaction the electrical diffusion constant was extracted for (Ga,Mn)As samples of different dimensionality. Using the Einstein relation allows us to deduce the effective density of states of (Ga,Mn)As at the Fermi energy.

13.
Phys Rev E Stat Nonlin Soft Matter Phys ; 63(6 Pt 2): 066701, 2001 Jun.
Article in English | MEDLINE | ID: mdl-11415252

ABSTRACT

A highly efficient algorithm for the reconstruction of microstructures of heterogeneous media from spatial correlation functions is presented. Since many experimental techniques yield two-point correlation functions, the restoration of heterogeneous structures, such as composites, porous materials, microemulsions, ceramics, or polymer blends, is an inverse problem of fundamental importance. Similar to previously proposed algorithms, the new method relies on Monte Carlo optimization, representing the microstructure on a discrete grid. An efficient way to update the correlation functions after local changes to the structure is introduced. In addition, the rate of convergence is substantially enhanced by selective Monte Carlo moves at interfaces. Speedups over prior methods of more than two orders of magnitude are thus achieved. Moreover, an improved minimization protocol leads to additional gains. The algorithm is ideally suited for implementation on parallel computers. The increase in efficiency brings new classes of problems within the realm of the tractable, notably those involving several different structural length scales and/or components.

14.
Phys Rev Lett ; 84(7): 1471-4, 2000 Feb 14.
Article in English | MEDLINE | ID: mdl-11017545

ABSTRACT

Slow structural relaxation ("aging") observed in many atomic, molecular, and polymeric glasses substantially alters their stress-strain relations and can produce a distinctive yield point. Using Monte Carlo simulation for a binary Lennard-Jones mixture, we have observed these phenomena and their cooling-rate dependences for the first time in an atomistic model system. We also observe that aging effects can be reversed by plastic deformation ("rejuvenation"), whereby the system is expelled from the vicinity of deep minima in its potential energy surface.

15.
J Magn Reson ; 128(2): 217-27, 1997 Oct.
Article in English | MEDLINE | ID: mdl-9356276

ABSTRACT

A method is proposed for the quantitative measurement of orientational anisotropy in glassy solids based on 2D dipolar NMR spectra with sample flipping (dipolar DECODER experiment). Purely dipolar spectra are obtained by chemical shift refocusing by a multiple pulse sequence. The experiment is applied to an investigation of a doubly 13C-labeled sample of bisphenol-A polycarbonate deformed in a channel-die apparatus. The orientational distribution function is determined by an expansion of the distribution in terms of spherical harmonics up to degree four.


Subject(s)
Magnetic Resonance Spectroscopy/methods , Polymers/chemistry , Anisotropy , Benzhydryl Compounds
16.
J Cutan Pathol ; 16(6): 370-4, 1989 Dec.
Article in English | MEDLINE | ID: mdl-2693505

ABSTRACT

We present a 73-year-old man with a 5-year history of dermatitis herpetiformis who developed lesions with the clinical, histologic, and immunologic features of bullous pemphigoid. Direct immunofluorescence testing of a skin biopsy demonstrated both granular deposition of IgA, predominantly in the papillary bodies, and linear deposition of IgG and C3 at the basement membrane zone. This mixed direct immunofluorescence pattern, typical for dermatitis herpetiformis in the type of IgA deposits, but also typical for pemphigoid in the linear localization of IgG and C3, is unusual. This case emphasizes that even after a specific diagnosis has been established, if the clinical morphology or response to therapy changes, repeat histologic and immunofluorescence studies may be indicated in diagnosis and management of patients with bullous disease.


Subject(s)
Dermatitis Herpetiformis/complications , Pemphigoid, Bullous/complications , Skin Diseases, Vesiculobullous/complications , Aged , Biopsy , Complement C3/metabolism , Dermatitis Herpetiformis/metabolism , Dermatitis Herpetiformis/pathology , Diagnosis, Differential , Fluorescent Antibody Technique , Humans , Immunoglobulin A/metabolism , Immunoglobulin G/metabolism , Male , Pemphigoid, Bullous/metabolism , Pemphigoid, Bullous/pathology , Skin/metabolism , Skin/pathology
17.
Am J Dermatopathol ; 11(2): 157-65, 1989 Apr.
Article in English | MEDLINE | ID: mdl-2712249

ABSTRACT

This paper presents a case of a cardiac myxoma with cutaneous emboli. The diagnosis of a cardiac lesion was anticipated after the histologic examination of a skin lesion. The first clue to the existence of a cardiac myxoma was a distinctive intravascular lesion of a dermal vessel. The clinical and pathologic features of cardiac myxoma are discussed. In addition, new evidence regarding the nature of a previously reported case of metastasizing cardiac myxoma is also presented.


Subject(s)
Embolism/pathology , Heart Neoplasms/pathology , Myxoma/pathology , Adult , Female , Heart Neoplasms/secondary , Humans , Myxoma/secondary , Skin/pathology
18.
Biochem J ; 198(2): 259-64, 1981 Aug 15.
Article in English | MEDLINE | ID: mdl-6275843

ABSTRACT

The nuclear envelope of seminal-vesicle epithelium was isolated by a procedure involving enzymic digestion with deoxyribonuclease I, sonication in the presence of 0.34 M-sodium citrate, and centrifugation through sucrose density gradients. The mass of envelope DNA was only 0.8% of that of envelope protein, and by transmission electron microscopy the envelope was 98-99% pure. We showed that the envelope possess a protein kinase activity which is uninfluenced by cyclic nucleotides. Both lysine-rich histone and dephosphophosvitin as substrates gave a greater specific activity than did envelope protein itself. Optimum requirements with respect to Na+, Mg2+, pH and ATP were established for each substrate, and the influence of other factors on enzyme activity was investigated. Data, obtained mainly with the use of lysine-rich histone, are presented which indicate that nuclear envelope from intact and 96 h-castrated guinea pigs may have equal protein kinase activities and, in separate experiments, equal phosphoprotein phosphatase activities. Clarification of these initial observations must await identification of the natural substrates or the envelope's phosphorylation-dephosphorylation reactions.


Subject(s)
Protein Kinases/metabolism , Seminal Vesicles/enzymology , Animals , Castration , Cell Fractionation , Electrophoresis, Polyacrylamide Gel , Epithelium/enzymology , Guinea Pigs , In Vitro Techniques , Male , Microscopy, Electron , Nuclear Envelope/enzymology , Nuclear Envelope/ultrastructure , Phosphoprotein Phosphatases/metabolism , Seminal Vesicles/ultrastructure
19.
J Urol ; 124(5): 615-6, 1980 Nov.
Article in English | MEDLINE | ID: mdl-6161257

ABSTRACT

Immunocytochemical discordance of human chorionic gonadotropin, alpha-fetoprotein and pregnancy specific beta-1 glycoprotein was studied in formaldehyde-fixed tissues of 26 patients with germinal testicular cancer. The cellular localization of these 3 markers has been correlated with the serum markers in the 26 patients. Serum alpha-fetoprotein, human chorionic gonadotropin and specific beta-1 glycoprotein were elevated in 15 of 26 (58 per cent), 17 of 26 (65 per cent) and 7 of 26 (27 per cent) patients, respectively, and in 22 of 26 (85 per cent) when all markers were considered. The cellular alpha-fetoprotein was localized in 5 of 26 (19 per cent), human chorionic gonadotropin in 12 of 26 (46 per cent) and specific beta-1 glycoprotein in 9 of 26 (35 per cent) patients. When all the markers were considered 15 of 26 patients (58 per cent) had either alpha-fetoprotein, human chorionic gonadotropin or specific beta-1 glycoprotein localized in the cancer cells.


Subject(s)
Chorionic Gonadotropin/analysis , Testicular Neoplasms/analysis , alpha-Fetoproteins/analysis , Choriocarcinoma/analysis , Choriocarcinoma/blood , Dysgerminoma/analysis , Dysgerminoma/blood , Histocytochemistry , Humans , Immunoenzyme Techniques , Male , Pregnancy-Specific beta 1-Glycoproteins/analysis , Teratoma/analysis , Teratoma/blood , Testicular Neoplasms/blood
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