Caregivers' experiences with the new family‐centred paediatric physiotherapy programme COPCA : a qualitative study

Caregivers' experiences during early intervention of their infant with special needs have consequences for their participation in the intervention. Hence, it is vital to understand caregivers' view. This study explored caregivers' experiences with the family-centred early intervention programme "COPing with and CAring for infants with special needs" (COPCA)

Emotion processing in infancy: specificity in risk for social anxiety and associations with two year outcomes

The current study examined the specificity of patterns of responding to high and low intensity negative emotional expressions of infants of mothers with social phobia, and their association with child outcomes at two years of age. Infants of mothers with social phobia, generalised anxiety disorder (GAD) or no history of anxiety were shown pairs of angry and fearful emotional expressions at 10 weeks of age. Symptoms of social withdrawal, anxiety and sleep problems were assessed at two years of age. Only infants of mothers with social phobia showed a tendency to look away from high intensity fear faces; however infants of mothers with both social phobia and GAD showed a bias towards high intensity angry faces. Among the offspring of mothers with social phobia, anxiety symptoms at two years of age were associated with a preference for high intensity fear faces in infancy. The reverse pattern was found amongst the offspring of non-anxious mothers. These findings suggest a possible specific response to emotional expressions among the children of mothers with social phobia

Variational Approach to Gaussian Approximate Coherent States: Quantum Mechanics and Minisuperspace Field Theory

This paper has a dual purpose. One aim is to study the evolution of coherent states in ordinary quantum mechanics. This is done by means of a Hamiltonian approach to the evolution of the parameters that define the state. The stability of the solutions is studied. The second aim is to apply these techniques to the study of the stability of minisuperspace solutions in field theory. For a $\lambda \varphi^4$ theory we show, both by means of perturbation theory and rigorously by means of theorems of the K.A.M. type, that the homogeneous minisuperspace sector is indeed stable for positive values of the parameters that define the field theory.Comment: 26 pages, Plain TeX, no figure

Sharp Metal-Insulator Transition in a Random Solid

We have measured zero temperature metallic conductivities above and below Mott's minimum value σ_(MIN) in bulk crystals of P doped Si. Studies of lattice heating, electronic heating and macroscopic inhomogeneities support the finding that conductivities below σ_(MIN) increase by over 10 as the P density is increased by 1%, and that over a wider density range the data can be fit t o a scaling form with a characteristic length that tends to diverge with the same exponent (ν = 0.55±0.10) in the metal and insulator

Measurements of conductivity near the metal-insulator critical point

We present measurements of the electrical conductivity at low temperatures of bulk samples of Si:P under uniaxial stress controlled to bring the samples within 0.1% of the metal-insulator transition. As the metal approaches the critical point, we find that the power law of the temperature correction to the conductivity predicted for weak Coulomb interactions continues to fit, but that its sign, size, and range of validity change. Its size defines a diffusion temperature which tends towards zero at the critical density, at which point the power law itself appears to change

Continuous and Discontinuous Quantum Phase Transitions in a Model Two-Dimensional Magnet

The Shastry-Sutherland model, which consists of a set of spin 1/2 dimers on a 2-dimensional square lattice, is simple and soluble, but captures a central theme of condensed matter physics by sitting precariously on the quantum edge between isolated, gapped excitations and collective, ordered ground states. We compress the model Shastry-Sutherland material, SrCu2(BO3)2, in a diamond anvil cell at cryogenic temperatures to continuously tune the coupling energies and induce changes in state. High-resolution x-ray measurements exploit what emerges as a remarkably strong spin-lattice coupling to both monitor the magnetic behavior and the absence or presence of structural discontinuities. In the low-pressure spin-singlet regime, the onset of magnetism results in an expansion of the lattice with decreasing temperature, which permits a determination of the pressure dependent energy gap and the almost isotropic spin-lattice coupling energies. The singlet-triplet gap energy is suppressed continuously with increasing pressure, vanishing completely by 2 GPa. This continuous quantum phase transition is followed by a structural distortion at higher pressure.Comment: 16 pages, 4 figures. Accepted for publication in PNA

Critical Behavior of the Conductivity of Si:P at the Metal-Insulator Transition under Uniaxial Stress

We report new measurements of the electrical conductivity sigma of the canonical three-dimensional metal-insulator system Si:P under uniaxial stress S. The zero-temperature extrapolation of sigma(S,T -> 0) ~\S - S_c\^mu shows an unprecidentedly sharp onset of finite conductivity at S_c with an exponent mu = 1. The value of mu differs significantly from that of earlier stress-tuning results. Our data show dynamical sigma(S,T) scaling on both metallic and insulating sides, viz. sigma(S,T) = sigma_c(T) F(\S - S_cT^y) where sigma_c(T) is the conductivity at the critical stress S_c. We find y = 1/znu = 0.34 where nu is the correlation-length exponent and z the dynamic critical exponent.Comment: 5 pages, 4 figure

High Resolution Study of Magnetic Ordering at Absolute Zero

High fidelity pressure measurements in the zero temperature limit provide a unique opportunity to study the behavior of strongly interacting, itinerant electrons with coupled spin and charge degrees of freedom. Approaching the exactitude that has become the hallmark of experiments on classical critical phenomena, we characterize the quantum critical behavior of the model, elemental antiferromagnet chromium, lightly doped with vanadium. We resolve the sharp doubling of the Hall coefficient at the quantum critical point and trace the dominating effects of quantum fluctuations up to surprisingly high temperatures.Comment: 5 pages, 4 figure

Optical response from terahertz to visible light of electronuclear transitions in LiYF_4:Ho^(3+)

Because of its role as a model system with tunable quantum fluctuations and quenched disorder, and the desire for optical control and readout of its states, we have used high-resolution optical absorption spectroscopy to measure the crystal-field excitations for Ho^(3+) ions in LiHo_xY_(1−x)F_4 from the terahertz to visible regimes. We show that many of the excitations yield very narrow lines visibly split even by the nuclear hyperfine interaction, making Ho^(3+) in LiHo_xY_(1−x)F_4 a candidate host for optically addressable electronuclear qubits with quality factors as high as Q = 4.7 × 10^5, where the higher-lying levels are electronic singlets. Optical transitions in the easily accessible near- and mid-infrared are narrow enough to allow readout of the ground-state electronuclear qubits responsible for the interesting magnetism of LiHo_xY_(1−x)F_4. While many of the higher-lying states have been observed previously, we also report here detailed spectra of terahertz excitations. The strengths of the electric and magnetic dipole crystal-field transition lines of five of the lowest excited spin-orbit manifolds of dilute LiYF_4:Ho^(3+) were calculated and compared with measurement. The magnitude of the nuclear hyperfine coupling was used to assign the correct upper and lower states to transition lines