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Is the information transmitted by an ensemble of neurons determined solely by the number of spikes fired by each cell, or do correlations in the emission of action potentials also play a significant role? We derive a simple formula which enables this question to be answered rigorously for short timescales. The formula quantifies the corrections to the instantaneous information rate which result from correlations in spike emission between pairs of neurons. The mutual information that the ensemble of neurons conveys about external stimuli can thus be broken down into firing rate and correlation components. This analysis provides fundamental constraints upon the nature of information coding - showing that over short timescales, correlations cannot dominate information representation, that stimulus-independent correlations may lead to synergy (where the neurons together convey more information than they would considered independently), but that only certain combinations of the different sources of correlation result in significant synergy rather than in redundancy or in negligible effects. This analysis leads to a new quantification procedure which is directly applicable to simultaneous multiple neuron recordings.

Alpha emitting radionuclides with medically relevant half-lives are interesting for treatment of tumors and other diseases because they deposit large amounts of energy close to the location of the radioisotope. Researchers at the Cyclotron Institute at Texas A&M University are developing a program to produce 211At, an alpha emitter with a medically relevant half-life. The properties of 211At make it a great candidate for targeted alpha therapy for cancer due to its short half-life (7.2 h). Astatine-211 has now been produced multiple times and reliability of this process is being improved.

We report a magnetic-resonance study of Gd-doped Eu2CuO4 single crystals. Cooling the samples in a magnetic field HFC, induces weak ferromagnetism (WF), with a strong out-of-plane anisotropy determined by the Dzyaloshinsky-Moriya (DM) interaction. In addition, there is in-plane anisotropy with an easy-axis parallel to the [110] crystal axis closest to HFC. An intense resonance mode is observed at the X band (9.5 GHz) when HFC is applied parallel to one of the 110 axes and the measuring field is rotated by 90°in the CuO2 plane. At the Q band (35 GHz), the in-plane resonance modes strongly depend on angle and temperature. We analyze the experimental results in terms of a phenomenological model for the magnetic free energy, which predicts a reorientation transition of the WF component of the magnetization mWF induced by the external field. Associated with this transition, a softening of the WF magnetic resonance mode occurs when the external field is applied perpendicular to the easy magnetization axis. The resulting angular variation of the resonance modes depends on whether the energy gap for the magnetic excitations is larger or smaller than the microwave energy. From the resonance data we have determined both the out-of-plane and in-plane anisotropy fields, HDM(T) and Hax(T), respectively. The extrapolated values for T=0 are HDM(0)=3.5(5)×105 G and Hax(0)=12(2) G. Both anisotropy fields decrease with increasing T, vanishing around TN243 K. The temperature dependence of the peak-to-peak linewidths, ΔHpp, measured at the X and Q bands is explained in terms of a temperature-independent frequency linewidth, Δω1/2/γ=1.6(2) kG. Nonresonant absorption losses around the maxima and minima of the ω/γ vs H curves are also described in terms of this finite width for the resonance modes. © 1993 The American Physical Society.

One unresolved question in the high-temperature superconductors and their copper oxide parent compounds is the absence of a Cu2+ electron-spin-resonance (ESR) signal even at temperatures well above the Néel temperature. We have extended the measurements up to 1150 K in both single crystals and ceramic pellets of La2CuO4+, 00.12, and no ESR signal has been observed. Our data are not compatible with the models based only on magnetic fluctuations which predict an ESR linewidth of a few hundred Oe at such high temperatures. Other suggested explanations for the absence of a Cu2+ ESR signal are discussed. © 1993 The American Physical Society.

We have measured the electron paramagnetic resonance (EPR) of Gd3+ in single crystals of La2-xSrxCuO4+δ, as a function of temperature T, magnetic-field angle, oxygen content, microwave frequency, and Sr concentration (0≤x≤0.024). For temperatures larger than the antiferromagnetic ordering temperature of the Cu lattice, TN, we have identified four different sites of Gd3+ as expected for twinned crystals and we are able to fit the data for all directions of the magnetic field. Samples annealed under vacuum or oxygen show only small changes on their crystal-field parameters and g values. For temperatures smaller than TN, the EPR lines are further split due to the internal magnetic field acting at the Gd site associated with the antiferromagnetic ordering of the Cu lattice. The temperature dependence of the splitting of the resonance lines allow us to calculate the moment per Cu ion. A value of ∼0.6μB per Cu ion at T=0 K is inferred, with the Cu moments lying in the bc plane about 5°from the c axis. The data only can be fit for all the directions of the applied magnetic field if other mechanisms such as a Heisenberg type of exchange between the Cu and Gd moments or a distortion of the lattice below TN are included. © 1993 The American Physical Society.

We report the observation of an unusual electron spin resonance (ESR) signal in single crystals of Eu2CuO4. The signal appears to be associated with a resonance mode of the CuO2 planes, similar to the midfield and low-field absorptions we have reported previously [Phys. Rev. B 41, 1934 (1990)]. However, it is only observed when the projection of the applied dc magnetic field in the CuO2 plane is within a few degrees of the 〈110〉 crystallographic direction. Additionally the sample must be field cooled in the CuO2 plane, but with a component of the cooling field perpendicular to the 〈110〉 ESR observation direction. Both the field for resonance and the linewidth exhibit a 1/cos θ dependence, where θ is the angle of the applied dc field between the c axis and the 〈110〉 observation direction. Additional constraints for observation of the resonance are that the microwave rf magnetic field must have a component in the CuO2 plane, but perpendicular to the dc field. The signal disappears above ∼215 K, which we assume is associated with the antiferromagnetic ordering temperature.

We have measured the EPR spectrum of dilute Gd3+ ions substituting for Eu3+ in Eu2CuO4. Each one of the resonance lines shows a splitting into two or more weaker lines below TN 215 K. The simultaneous appearance of a low-field microwave-absorption signal is attributed to the onset of long-range antiferromagnetic ordering with a weak ferromagnetic component. The splitting of the EPR spectrum is associated with different Gd sites in the magnetically ordered structure. A reduction of the local symmetry of the rare-earth sites below TN is described in terms of an internal magnetic field lying in the ab plane and additional crystal-field terms related to local crystallographic distortions. Dipolar and exchange contributions to the internal field are discussed. Possible random static displacements of the oxygen atoms in the CuO2 planes and their role in the development of the weak ferromagnetism and the presence of internal fields at the Gd sites are also analyzed. A strong dependence of the Gd EPR spectrum and the microwave absorption on the magnetic history of the samples has been observed, suggesting the formation of magnetic domains or a glassy state. © 1991 The American Physical Society.

The low-temperature (T

We report the results of an extensive investigation of the magnetic properties of a large series of undoped R2CuO4 single crystals with R==Pr, Nd, Sm, Eu, and Gd (which are the host compounds for the newly discovered series of electron cuprate superconductors) and mixture versions of the form A2-xBxCuO4, with A==Pr, Nd, Sm, Eu, or Gd, and B==Gd, Tb, or Dy. We have measured dc and ac magnetization, microwave magnetoabsorption, EPR, and specific heat. These measurements reveal two characteristic transition temperatures associated with a novel complex magnetic behavior, including weak ferromagnetism, two sharp peaks in the low-field dc magnetization, an unusual anisotropy in the EPR resonance field for R=Gd, and two additional anisotropic microwave absorption modes. The higher characteristic transition temeperature at 270 K is associated with antiferromagnetic ordering of the Cu moments which are strongly coupled within the CuO2 layers. The lower, at 20 K, cannot be attributed to antiferromagnetic ordering of the R moments and is tentatively attributed to a spontaneous canted spin reorientation. An understanding of this magnetic behavior is important in order to ascertain its relationship to possible mechanisms of high-temperature superconductivity. © 1990 The American Physical Society.

OBJECTIVE: To investigate micronutrient supply in phenylketonuria (PKU) patients on a relaxed diet. SUBJECTS/METHODS: Sixty-seven patients (6-45 years) with a phenylalanine tolerance ≥600 mg/day were included in the study. From a 3-day diet record, protein supply as well as consumption of essential amino acids and several micronutrients were assessed and compared with the current recommendations and data for the healthy population. RESULTS: Protein supply and consumption of all essential amino acids were sufficient in all patients. Supply of micronutrients depended on dietary regime. Patients with a total protein supply of 120% or more of the recommended amount and at least 0.5 g protein per kg body weight from amino-acid mixture (AAM) were sufficiently supplied with all investigated micronutrients. All patients without AAM supplement showed severe micronutrient deficiencies in their diet records. CONCLUSION: PKU patients under a relaxed diet are at risk of an insufficient nutrient supply, if they have first no substitution with AAM, second a protein supply less than 0.5 g per kg body weight from AAM or third a total protein supply less than 120% of the recommendations. Therefore, close monitoring, specific dietary counseling and potential supplementation is mandatory to prevent micronutrient deficiencies in PKU patients. European Journal of Clinical Nutrition (2014) 68, 119-124; doi: 10.1038/ejcn.2013.218; published online 20 November 2013 Keywords: Phenylketonuria; relaxed diet; micronutrient deficiencies; micronutrients, INTRODUCTION Phenylketonuria (PKU;OMIN 261600) is one of the most common inborn metabolic disorders, with an incidence varying between 1:3000 and 1:30000 across Europe. (1) It is caused by a deficient [...]