Soft Spin Research Articles

Dynamical Equation Approach to Protein Design

A new approach to protein design is proposed. Our dynamical equation approach is based on the criterion by Kurosky and Deutsch, 1), 2) with which the probability of a target structure in a conformation space is maximized at low but finite temperature. The key feature of the proposed approach is soft spin representation of monomer variables that leads to the “design equation”. 3) The advantage of the present approach is its parallel evolution of the monomer sequence variables and the resulting rapid convergence. We review the recent development of design schemes, implement numerical simulations by the design equation for the generalized HP model, 24), 26), 27) and compare the performance with an algorithm based on the simulated annealing in sequence space.

Two-Day Collection and Pooling of Peripheral Blood Stem Cells with Semiautomated Density Gradient Cell Separation

Autologous and allogeneic PBSC collection and cryopreservation have been shown to be feasible in the pediatric population. This technique may be associated with complications, including volume overload and DMSO toxicity. To decrease these risks, we developed a technique by which PBSC are collected over a 2-day period and pooled prior to cryopreservation. PBSC are harvested on day 1 and stored with tissue culture medium on a rocker at ambient temperature. On day 2, a second PBSC harvest is performed, and the two harvests are pooled, separated on a Ficoll gradient in a semiautomatic closed system, and frozen with 10% DMSO after a soft spin for volume reduction. Cells from each day's harvest are tested for cell count and viability. A total of 36 collections in 26 patients were performed. This technique resulted in a 73%+/-0.0% reduction in volume (mean +/- SEM) and an 88%+/-0.9% depletion of RBC. Mononuclear cell (MNC) count recovery was 88%+/-2.6%, and the MNC dose delivered to the patient was 3.1+/-0.6x10(8) cells/kg. Cell viability was >98% before and after processing. Seventeen patients have been transplanted thus far, and all these patients engrafted with minimal toxicity. These data indicate that storing PBSC for up to 24 h after harvest does not decrease PBSC viability or delay engraftment.

Preparation of Leukodepleted Platelet Concentrates from Pooled Buffy Coats: Prestorage Filtration with Autostop™BC

Background and Objectives: Our requirements for leukocyte–depleted platelet concentrates (LD–PC) for an adult patient are: platelets >240×10⁹, leukocytes <5×10⁶, volume of 150–400 ml; and at the end of storage a pH between 6.8 and 7.4 and presence of the swirling effect. Our aim was to develop a standardized, semiautomated method for the production of LD–PC, by pooling of buffy coats (BC), and prestorage leukoreduction by filtration. Materials and Methods: Whole blood was collected in Top and Bottom systems, and separated automatically with the Compomat^™ G3 equipment into a red cell concentrate, a plasma and a BC. Subsequently, a pool of 5 BC was made, and 200 g plasma from one of the donors was added. Then, after soft spin centrifugation, the platelet rich plasma was leukocyte depleted by filtration using the Autostop^™BC filter, and stored in a 1,000 ml polyolefin platelet storage bag. Results: BC (n = 60) had a volume of 51±2 ml (mean ± SD) with a hematocrit of 0.44±0.03 l/l and contained 80±5% of the platelets and 74±12% of the leukocytes of the whole blood. Routinely prepared LD–PC (n = 15,037) contained a median of 341×10⁹ platelets (range 49–599×10⁹), with only 104/15,037 (0.7%) containing fewer than 240×10⁹ platelets; the median volume was 263 ml (range 134–373 ml). In 118/917 (13%) LD–PC leukocytes were observed in the Nageotte hemocytometer, but only twice exceeding 1×10⁶ leukocytes per unit, and none exceeding 5×10⁶ (median <0.6×10⁶; range <0.6–1.41×10⁶). Storage experiments of the LD–PC (n = 12) revealed adequate oxygenation and maintenance of pH and swirling effect up to 9 days. Conclusions: This method warrants with 99% confidence that LD–PC contain more than 240×10⁹ platelets; with 97.5% confidence that 100% of the LD–PC contain <5×10⁶ leukocytes, and with 95% confidence that more than 99% of the LD–PC contain fewer than 1×10⁶ leukocytes; these LD–PC can be stored satisfactorily for up to 9 days.

Preparation of Leukodepleted Platelet Concentrates from Pooled Buffy Coats: Prestorage Filtration with Autostop™BC

Abstract Background and Objectives: Our requirements for leukocyte‐depleted platelet concentrates (LD‐PC) for an adult patient are: platelets &gt;240×109, leukocytes &lt;5×106, volume of 150–400 ml; and at the end of storage a pH between 6.8 and 7.4 and presence of the swirling effect. Our aim was to develop a standardized, semiautomated method for the production of LD‐PC, by pooling of buffy coats (BC), and prestorage leukoreduction by filtration. Materials and Methods: Whole blood was collected in Top and Bottom systems, and separated automatically with the Compomat™ G3 equipment into a red cell concentrate, a plasma and a BC. Subsequently, a pool of 5 BC was made, and 200 g plasma from one of the donors was added. Then, after soft spin centrifugation, the platelet rich plasma was leukocyte depleted by filtration using the Autostop™ BC filter, and stored in a 1,000 ml polyolefin platelet storage bag. Results: BC (n = 60) had a volume of 51±2 ml (mean ± SD) with a hematocrit of 0.44±0.03 I/I and contained 80±5% of the platelets and 74±12% of the leukocytes of the whole blood. Routinely prepared LD‐PC (n = 15,037) contained a median of 341×109 platelets (range 49‐599×109), with only 104/15,037 (0.7%) containing fewer than 240×109 platelets; the median volume was 263 ml (range 134‐373 ml). In 118/917 (13%) LD‐PC leukocytes were observed in the Nageotte hemocytometer, but only twice exceeding 1×106 leukocytes per unit, and none exceeding 5×106 (median &lt;0.6×106; range &lt;0.6‐1.41×106). Storage experiments of the LD‐PC (n = 12) revealed adequate oxygenation and maintenance of pH and swirling effect up to 9 days. Conclusions: This method warrants with 99% confidence that LD‐PC contain more than 240×109 platelets; with 97.5% confidence that 100% of the LD‐PC contain &lt;5×106 leukocytes, and with 95% confidence that more than 99% of the LD‐PC contain fewer than 1×106 leukocytes; these LD‐PC can be stored satisfactorily for up to 9 days.

The Role of Polarons in Ferroelectric Phase Transitions

We present a microscopic theory of ferroelectric phase transitions and off-center displacements in perovskites. We show that the inclusion of strong intraband electron–phonon interaction (i.e., the existence of small polarons) into the framework of the interband theory of displasive like ferroelectrics, leads to local, spinlike structural distortions in the paraelectric phase. Their interaction with the soft mode induces spin–spin coupling through the soft phonon leading to a spin ordering phase transition. The resulting theory is shown to quantitatively explain both displasive-like and order–disorder-like features in two representative perovskites: KNbO3 and PbTiO3.

Design Equation: A Novel Approach to Heteropolymer Design

A novel approach to heteropolymer design is proposed. It is based on the criterion by Kurosky and Deutsch, with which the probability of a target conformation in a conformation space is maximized at low but finite temperature. The key feature of the proposed approach is the use of soft spins (fuzzy monomers) that leads to a design equation, which is an analog of the Boltzmann machine learning equation in the design problem. We implement an algorithm based on the design equation for the generalized HP model on the 3×3×3 cubic lattice and check its performance.

Preparation and preservation of red cells.

The production of blood components has undergone several changes during the last decades. Red blood cells will have slightly different properties depending on the way of preparation: whether a hard or soft spin has been used, whether platelets and/or leukocytes have been removed or not, and whether the red cells have been suspended in part of the original plasma or in an additive solution. Automated techniques are now often used for the separation of buffy coats, red cells and plasma. Recently, apheresis techniques have been applied for the preparation of red cells, mostly in combination with plasma or platelets. Continuous addition of the anticoagulant during collection reduces the delay between collection and separation, but the cost is higher and donor time longer. Most of the methods for the preparation and storage of red cells allow 35-42 days of storage with a mean in vivo recovery of > 75%. However, the content of erythrocyte 2,3-DPG is commonly lost within 1-2 weeks, caused by the accumulation of acid metabolites, but can be maintained longer with new systems of storage. Leukodepletion of red cells by filtration is used increasingly, but its importance in the majority of transfusions is still unclear. New options for the preparation and storage of red blood cells are available and undergo continuous evaluation.

Noise-induced phase transition in soft Ising spins with a fluctuating interaction

We investigate noise-induced phase transitions in soft Ising spins, which have continuous values, with a fluctuating interaction within the framework of the mean-field scheme. The fluctuating interaction provides an effective ferromagnetic coupling, leading to a ferromagnetic order. The interplay of the fluctuating interaction and an additive noise leads to a reentrant transition, triple transitions, and a softening of the order parameter, presenting a weak order in the ordered phase. In the limit of Ising spins the fluctuating interaction renormalizes the mean field, reducing the critical intensity of the additive noise.

Kondo lattice model: Unitary transformations, spin dynamics, strongly correlated charged modes, and vacuum instability

Using unitary transformations, we express the Kondo lattice Hamiltonian in terms of an optimal set of canonical operators obtaining an effective Hamiltonian which, for small couplings, consists of a kinetic term for electrons and holes, an RKKY term, and a renormalized Kondo interaction. The physical picture of the system implied by this formalism is that of a vacuum state consisting of a background of RKKY-induced spin correlations, where two kinds of elementary modes can be excited: soft neutral modes associated with deformations of the spin liquid, and charged modes corresponding to the excitation of electrons and holes. We study the charged modes, finding, apart from the ‘normal’, uncorrelated states, strongly correlated modes involving soft electrons (or holes) and spin fluctuations, which strongly renormalize the low-energy charged spectrum, and whose energy becomes negative beyond a critical coupling, signaling a vacuum instability and a transition to a new phase.

Thermal noise with 1/f spectral density in the random anisotropy system DyNi

It has been extensively reported in the last few years on the existence of thermal noise with 1/f spectrum in a variety of magnetic systems at low temperature including soft ferromagnetic alloys, spin glasses and high T c superconductors. Here we report on the detection of the same phenomenon in DyNi 1.32 a random anisotropy amorphous alloy.

Reply to "Comment on 'Dynamics of Heisenberg ferromagnets at low temperature' "

The linewidth of the soft spin wave and the dynamic scaling hypothesis are discussed for a low-dimensional Heisenberg ferromagnet in reply to Reiter's comment.

Magnetoresistance in a strongly interacting two-dimensional metal.

Using a gauge-theory formulation of the fluxless metallic phase of the t-J model in two dimensions, it is shown that the soft chiral spin fluctuations existing in this phase are suppressed by the introduction of a small transverse magnetic field, while soft charge fluctuations are enhanced. This effect results in the reduction of the predicted linear-in-temperature resistance by an amount proportional to the square of the Hall conductance in the strong-correlation limit near half filling. However, away from this limit, the magnetoresistance may be positive. A similar effect is also shown to exist for the thermal resistance and the specific heat. A comparison with available data on the oxide superconductors is made.

Normal state properties in the cuprates and their Fermi liquid based interpretation

Abstract A central issue in the field of high temperature superconductivity is the nature of the normal state. Here we review normal state transport, thermodynamic, magnetic and spectroscopic data and discuss their interpretation within a Fermi liquid based framework. Comparison with other highly correlated systems, such as the heavy fermnion metals and the quantum liquid 3 He, is also presented. It is demonstrated that the cuprate data are not consistent with canonical Fermi liquid behavior. However, if the Fermi liquid is characterized by low energy scales, arising from narrow bandwidths or soft spin fluctuations, then canonical behavior is not expected at the relatively “high” temperatures of the normal state. In this way anomalies above T c may be reconciled with a Fermi liquid (ground state) picture. Here we review the two main Fermi liquid based schools and their interpretation of the data. These are the ”almost localized” and “almost magnetic” Fermi liquid descriptions. The dichotomy between these two nearinstabilities has appeared in the context of the heavy fermoins as well as liquid 3 He and seems to be generally associated with highly correlated systems. Both approaches have addressed the data with some success and it is clear that they are, in many respects, closely related. The relationship between other Fermi-liquid-like, as well as more unconventional schemes is also addressed. Here it is claimed that the strongest support for a Fermi liquid based approach to the cuprates derives from the comparison with other strongly correlated Fermi liquid systems, which exhibit similar normal state anomalies.

From fermiology to spin dynamics: Current status of Fermi liquid based approaches to the cuprates

A central issue in the field of high temperature superconductivity is the nature of the normal state. Here we review normal state transport, thermodynamic, magnetic and spectroscopic data and discuss their interpretation within a Fermi liquid based framework. Il is demonstrated that the cuprate data are not consistent with canonical Fermi liquid behavior. However, if the Fermi liquid is characterized by low energy scales, arising from narrow bandwidths or soft spin fluctuations, then canonical behavior is not expected at the relatively “high” temperatures of the normal state. We discuss two main Fermi liquid based schools, i.e., the “almost localized” and “almost magnetic” descriptions. Both approaches have addressed the data with some success and it is clear that they are, in many respects, closely related. Here it is claimed that the strongest support for a Fermi liquid based approach to the cuprates derives from the comparison with other strongly correlated Fermi liquid systems, which exhibit similar normal state anomalies.

Magnetovolume Effects in Strongly and Intermediately Correlated Elecron Systems

Analyses of magnetovolume effects such as the forced volume magnetostriction and the thermal expansion anomaly can give estimation of local amplitude of spin fluctuations. We have shown that bee Fe has a rigid magnetic moment and that the magnetic moment of Invar type alloys is rather soft. It is pointed out that the total energy difference between the magnetized state and the nonmagnetic state obtained by self-consistent energy band calcula­ tions using a local-spin-density approximation is much higher than the Curie temperature for rigid spin systems and comparable for soft spin systems. The effects of zero point spin fluctuations observed in the YMn2 system are discussed.

Symmetry analysis of the antiferromagnetic phase transitions in hexagonal FeGe

In hexagonal FeGe the experimental data show existence of three ordered magnetic phases. A symmetry analysis based on the representations of the space group of the crystal structure is applied in order to predict the possible magnetic structures of hexagonal FeGe. The character of the transitions between the different magnetic structures is considered by expressing the phenomenological Ginzburg-Landau functionals in terms of the order parameters for the different phases. The magnetic modes for the wave-vector k allowed by the symmetry are also calculated. Along with a possible collinear magnetic ordering in the basal plane, clockwise and anti-clockwise triangular ordering of the basal-plane spin components are suggested. The presently available experimental data does not allow a choice between different types of basal-plane ordering. In addition, the spin wave modes for the wave-vector q along the c axis are calculated and the symmetry relations between the spin waves and the magnetic modes with wave-vector k are established. This allows the authors to suggest that the observed magnetic ordering of the basal-plane spin components at T2<TN may be caused by condensation of the corresponding spin wave in the antiferromagnetic phase. Such condensation is the result of a soft spin wave at wave-vector q=k which might be observed experimentally.

The phase transition of spin glasses in an external AC field

By means of the soft spin version of the SK spin glass the phase transition in an external AC field is investigated. It is shown that a well defined phase transition temperature Tc exists and depends on the amplitude hAC and frequency nu of the AC field. The dynamical AC non-linear susceptibility chi 2(3 nu ) exhibits a peak at Tc whose height and width are proportional to nu -1/2 and nu 1/2 respectively.

Protein adsorption on soft contact lenses: III. Mucin

Adsorption of bovine submaxillary mucin (BSM) on three different soft contact surfaces, lathe cut (LC) and spin cast (SC) crosslinked poly-2-hydroxyethylmethacrylate and spin cast poly(2-hydroxyethylmethacrylate/methacrylic acid) (PHEMA/MAA), was studied. The in vitro process was followed by attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). A three-layer structure is envisaged for the adsorbed BSM: a very thin surface layer of strongly bound and conformationally altered mucin constitutes the surface layer. A random to β-sheet structural transition activated by the hydrogel surface is proposed for this layer. Glycoprotein hydrogen-bonding with the polymer hydroxyls and interaction of charged and hydrophobia groups with hydrogel surfaces are important in stabilizing this layer. Most of the adsorbed BSM (99%) is found in the middle and top layers which are formed by a different degree of associated BSM (their conformation is minimally changed or not changed at all, respectively) and are weakly adsorbed to the lens surfaces. Surface morphololgy and chemical composition of the lenses are important adsorption parameters only for the reversibly adsorbed BSM.

Dynamic scaling for spin glasses near the de Almeida-Thouless line

We calculate the dynamic local susceptibility χ(ω) of an Ising spin glass near the de Almeida-Thouless (AT) line within the soft spin dynamics for the Sherrington-Kirkpatrick model. We find a crossover from analytic behaviour of χ(ω) at ω=0 above the AT line to a power law behaviour χ(ω)α(−iω) v on the AT line and discuss the analytic properties of the crossover function. The frequencyscale is proportional toθ 1/v , where ρ measures the distance from the AT line. We determine the spectrum of relaxation times which diverge asθ 1−1/v . The average relaxation time diverges asθ −1/v wherev≦1/2. In addition we determine the absolute frequency scale and prove the consistency of the ansatz of Sompolinsky and Zippelius χ(ω)−χ(0)α(−iω) v at and below the AT line.

E-mode splitting in the ferroelectric phase of the ferroelectric arsenates

Young and Elliott1 have recently extended the pseudospin model to include coupling between the soft spin wave mode and fluctuations in the phonon density via two phonon terms in the Hamiltonian. One of the consequences of this approach is that the pseudospin-two phonon coupling leads to a splitting of the E modes in addition to any restrahlen splitting. We report on light scattering investigations of the E mode spectra in the ferroelectric phase of the arsenate family for k along the basal planes (0, 0, 1), (1, 1,0) and (1,0,0). The results reveal small but finite E-mode splittings arising from non-restrahlen effects. These results are discussed in terms of the pseudospin-two phonon model.