Free energies in the presence of electric and magnetic fields

We discuss different free energies for materials in static electric and magnetic fields. We explain what the corresponding Hamiltonians are, and describe which choice gives rise to which result for the free energy change, dF, in the thermodynamic identity. We also discuss which Hamiltonian is the most appropriate for calculations using statistical mechanics, as well as the relationship between the various free energies and the "Landau function", which has to be minimized to determine the equilibrium polarization or magnetization, and is central to Landau's theory of second order phase transitions

Atom lithography without laser cooling

Using direct-write atom lithography, Fe nanolines are deposited with a pitch of 186 nm, a full width at half maximum (FWHM) of 50 nm, and a height of up to 6 nm. These values are achieved by relying on geometrical collimation of the atomic beam, thus without using laser collimation techniques. This opens the way for applying direct-write atom lithography to a wide variety of elements.Comment: 7 pages, 11 figure

The association between parenting behavior and somatization in adolescents explained by physiological responses in adolescents

Introduction: This study adds to the knowledge on somatization in adolescents by exploring its relation with parenting behavior and the mediating/moderating role of physiological responses in adolescents to parenting behavior. Method: Eighteen adolescents with high and 18 adolescents with low somatization scores and their mothers completed a discussion task, from which observed parenting behavior scores were derived. Skin conductance in adolescents was measured before and during the discussion. Results: For adolescents with high levels of physiological responses, unadaptive parenting was related to a higher chance of high somatization scores. For low physiologically responsive adolescents, the relation between parenting behavior and somatization was not significant. Conclusion: Parenting behavior is not univocally related to somatization in adolescents, but the association depends on physiological responses in adolescents. (C) 2014 Elsevier B.V. All rights reserved

Bottom-up versus top-down: Effective connectivity reflects individual differences in grapheme-color synesthesia

In grapheme-color synesthesia, letters elicit a color. Neural theories propose that synesthesia is due to changes in connectivity between sensory areas. However, no studies on functional connectivity in synesthesia have been published to date. Here, we applied psycho-physiological interactions (PPI) and dynamic causal modeling (DCM) in fMRI to assess connectivity patterns in synesthesia. We tested whether synesthesia is mediated by bottom-up, feedforward connections from grapheme areas directly to perceptual color area V4, or by top-down feedback connections from the parietal cortex to V4. We took individual differences between synesthetes into account: 'projector'synesthetes experience their synesthetic color in a spatial location, while 'associators'only have a strong association of the color with the grapheme. We included 19 grapheme-color synesthetes (14 projectors, 5 associators) and located group effects of synesthesia in left superior parietal lobule (SPL) and right color area V4. With PPI, taking SPL as a seed region, we found an increase in functional coupling with visual areas (also V4), for the synesthesia condition. With PPI, however, we can not determine the direction of this functional coupling. Based on the GLM results, we specified 2 DCMs to test whether a bottom-up or a top-down model would provide a better explanation for synesthetic experiences. Bayesian Model Selection showed that overall, neither model was much more likely than the other (exceedance probability of 0.589). However, when the models were divided according to projector or associator group, BMS showed that the bottom-up, feedforward model had an exceedance probability of 0.98 for the projectors: it was strongly preferred for this group. The top-down, feedback model was preferred for the associator group (exceedance probability = 0.96). To our knowledge, we are the first to report empirical evidence of changes in functional and effective connectivity in synesthesia. Whether bottom-up or top-down mechanisms underlie synesthetic experiences has been a long-time debate: that different connectivity patterns can explain differential experiences of synesthesia may greatly improve our insight in the neural mechanisms of the phenomenon

Long-Ranged Orientational Order in Dipolar Fluids

Recently Groh and Dietrich claimed the thermodynamic state of a dipolar fluid depends on the shape of the fluid's container. For example, a homogeneous fluid in a short fat container would phase separate when transferred to a tall skinny container of identical volume and temperature. Their calculation thus lacks a thermodynamic limit. We show that removal of demagnetizing fields restores the true, shape independent, thermodynamic limit. As a consequence, spontaneously magnetized liquids display inhomogeneous magnetization textures.Comment: 3 pages, LaTex, no figures. Submitted as comment to PRL, May 199

Beyond the surface: Imaging of (sub)clinical joint changes in haemophilia

Haemophilia is an X-linked inherited coagulation disorder that results in an increased bleeding tendency. Most bleeding occurs in the large synovial joints (elbows, knees, ankles). Recurrent joint bleeding eventually leads to irreversible haemophilic arthropathy, which causes pain and reduces functionality and quality of life. Prophylactic treatment prevents most bleeding episodes. However, (subclinical) joint bleeding and inflammation still occur. Surprisingly, even in the absence of clinically overt joint bleeding, long-term progression to arthropathy is observed. Subclinical bleeding and inflammation are therefore thought to contribute to the development of arthropathy. Early detection of these subclinical processes is becoming increasingly important in the prevention of arthropathy as overt joint bleeding becomes rare with new replacement therapies. This thesis focused on the detection of subclinical bleeding, the screening for subclinical joint inflammation, and the use of ultrasound in the management of acute joint episodes. The first part of this thesis discussed the detection of subclinical bleeding. Chapter 2 demonstrated that quantitative MRI T1 and T2 relaxometry can differentiate between haemorrhagic joint effusion with low blood concentration and synovial fluid in vitro. Chapter 3 demonstrated good feasibility and reproducibility of the T2-relaxometry method at 3 Tesla in vivo. Chapter 4 describes evidence for subclinical joint bleeding in people with severe haemophilia on long-term prophylaxis. Conventional MRI of joints without a history of bleeding showed evidence of previous subclinical bleeding in 16% of people with severe haemophilia A on prophylaxis. The second part of this thesis focused on screening for subclinical joint inflammation. Chapters 5 and 6 are devoted to screening for (subclinical) synovial proliferation as a proxy for joint inflammation. The literature review in Chapter 5 showed that physical examination underestimates the prevalence of ultrasound-detected synovial proliferation. Therefore, ultrasound appears to have added value in screening for subclinical synovial hypertrophy. The findings in Chapter 6 support the value of ultrasound screening for subclinical synovial proliferation. The role of ultrasound is further emphasized by the failure of biochemical markers to identify ultrasound-detected subclinical synovial proliferation. The third part of this thesis discusses the use of ultrasound in management of acute joint episodes. Although subclinical joint disease can be detected by imaging, its impact on patient management remained unclear. The cross-sectional study in Chapter 7 described that ultrasound, when added to clinical assessment, often changed the diagnosis and treatment of acute musculoskeletal complaints in people with haemophilia and von Willebrand disease (VWD). In Chapter 8, ultrasound and physical examination were used to monitor the recovery of joint bleeding in people with haemophilia and VWD. Ultrasound and physical examination provided complementary information in monitoring joint bleed recovery. In conclusion, ultrasound should be used in haemophilia care as a screening tool for (subclinical) joint damage, as a diagnostic tool for acute joint episodes, and as a monitoring tool for recovery from joint bleeding. MRI remains the reference standard for imaging early joint changes in haemophilia and is therefore best used as a troubleshooter in difficult clinical cases and as a sensitive outcome measure in research

Spin Stiffness in the Hubbard model

The spin stiffness $\rho_{\rm s}$ of the repulsive Hubbard model that occurs in the hydrodynamic theory of antiferromagnetic spin waves is shown to be the same as the thermodynamically defined stiffness involved in twisting the order parameter. New expressions for $\rho_{\rm s}$ are derived, which enable easier interpretation, and connections with superconducting weight and gauge invariance are discussed.Comment: 21 Pages LaTeX2e, to be published in Journal of Physics

Ensemble Theory for Force Networks in Hyperstatic Granular Matter

An ensemble approach for force networks in static granular packings is developed. The framework is based on the separation of packing and force scales, together with an a-priori flat measure in the force phase space under the constraints that the contact forces are repulsive and balance on every particle. In this paper we will give a general formulation of this force network ensemble, and derive the general expression for the force distribution $P(f)$. For small regular packings these probability densities are obtained in closed form, while for larger packings we present a systematic numerical analysis. Since technically the problem can be written as a non-invertible matrix problem (where the matrix is determined by the contact geometry), we study what happens if we perturb the packing matrix or replace it by a random matrix. The resulting $P(f)$'s differ significantly from those of normal packings, which touches upon the deep question of how network statistics is related to the underlying network structure. Overall, the ensemble formulation opens up a new perspective on force networks that is analytically accessible, and which may find applications beyond granular matter.Comment: 17 pages, 17 figure

Electrochemical methods for speciation of trace elements in marine waters. Dynamic aspects

The contribution of electrochemical methods to the knowledge of dynamic speciation of toxic trace elements in marine waters is critically reviewed. Due to the importance of dynamic considerations in the interpretation of the electrochemical signal, the principles and recent developments of kinetic features in the interconversion of metal complex species will be presented. As dynamic electrochemical methods, only stripping techniques (anodic stripping voltammetry and stripping chronopotentiometry) will be used because they are the most important for the determination of trace elements. Competitive ligand ex- change-adsorptive cathodic stripping voltammetry, which should be considered an equilibrium technique rather than a dynamic method, will be also discussed because the complexing parameters may be affected by some kinetic limitations if equilibrium before analysis is not attained and/or the flux of the adsorbed complex is in fluenced by the lability of the natural complexes in the water sample. For a correct data interpretation and system characterization the comparison of results obtained from different techniques seems essential in the articulation of a serious discussion of their meaning