The order parameter-entropy relation in some universal classes: experimental evidence

The asymptotic behaviour near phase transitions can be suitably characterized by the scaling of $\Delta s/Q^2$ with $\epsilon=1-T/T_c$, where $\Delta s$ is the excess entropy and $Q$ is the order parameter. As $\Delta s$ is obtained by integration of the experimental excess specific heat of the transition $\Delta c$, it displays little experimental noise so that the curve $\log(\Delta s/Q^2)$ versus $\log\epsilon$ is better constrained than, say, $\log\Delta c$ versus $\log\epsilon$. The behaviour of $\Delta s/Q^2$ for different universality classes is presented and compared. In all cases, it clearly deviates from being a constant. The determination of this function can then be an effective method to distinguish asymptotic critical behaviour. For comparison, experimental data for three very different systems, Rb2CoF4, Rb2ZnCl4 and SrTiO3, are analysed under this approach. In SrTiO3, the function $\Delta s/Q^2$ does not deviate within experimental resolution from a straight line so that, although Q can be fitted with a non mean-field exponent, the data can be explained by a classical Landau mean-field behaviour. In contrast, the behaviour of $\Delta s/Q^2$ for the antiferromagnetic transition in Rb2CoF4 and the normal-incommensurate phase transition in Rb2ZCl4 is fully consistent with the asymptotic critical behaviour of the universality class corresponding to each case. This analysis supports, therefore, the claim that incommensurate phase transitions in general, and the A$_2$BX$_4$ compounds in particular, in contrast with most structural phase transitions, have critical regions large enough to be observable.Comment: 13 pp. 9 ff. 2 tab. RevTeX. Submitted to J. Phys.: Cond. Matte

Fast relaxation in a fragile liquid under pressure

The incoherent dynamic structure factor of ortho-terphenyl has been measured by neutron time-of-flight and backscattering technique in the pressure range from 0.1 MPa to 240 MPa for temperatures between 301 K and 335 K. Tagged-particle correlations in the compressed liquid decay in two steps. The alpha-relaxation lineshape is independent of pressure, and the relaxation time proportional to viscosity. A kink in the amplitude f_Q(P) reveals the onset of beta relaxation. The beta-relaxation regime can be described by the mode-coupling scaling function; amplitudes and time scales allow a consistent determination of the critical pressure P_c(T). alpha and beta relaxation depend in the same way on the thermodynamic state; close to the mode-coupling cross-over, this dependence can be parametrised by an effective coupling Gamma ~ n*T**{-1/4}.Comment: 4 Pages of RevTeX, 4 figures (submitted to Physical Review Letters

Universal mechanism of discontinuity of commensurate-incommensurate transitions in three-dimensional solids: Strain dependence of soliton self-energy

We show that there exists a universal mechanism of long-range soliton attraction in three-dimensional solids and, therefore, of discontinuity of any commensurate-incommensurate (C-IC) phase transition. This mechanism is due to the strain dependence of the soliton self-energy and specific features of the solid-state elasticity. The role of this mechanism is studied in detail for a class of C-IC transitions where the IC modulation is one-dimensional, the anisotropy in the order parameter space is small, and the symmetry of the systems allows the existence of the Lifshitz invariant. Two other mechanisms of soliton attraction are operative here but the universal mechanism considered in this paper is found to be the most important one in some cases. Comparison with the most extensively studied C-IC transition in $\rm K_2SeO_4$ shows that the experimentally observed thermal anomalies can be understood as a result of the smearing of the theoretically predicted discontinuous transition.Comment: 8 pages (extended version, title changed

Unconventional magnetic transition and transport behavior in Na0.75CoO2

Here we report an unconventional magnetic and transport phenomenon in a layered cobalt oxide, NaxCoO2. Only for x = 0.75, a magnetic transition of the second order was clearly detected at Tm ~ 22 K where an apparent specific-heat jump, an onset of extremely small spontaneous magnetization, and a kink in resistivity came in. Moreover large positive magnetoresistance effect was observed below Tm. These features of the transition strongly indicate the appearance of an unusual electronic state that may be attributed to the strongly-correlated electrons in Na0.75CoO2.Comment: 5 pages, 6 figures, to appear in Phys. Rev.

Nuclear magnetic relaxation and superfluid density in Fe-pnictide superconductors: An anisotropic \pm s-wave scenario

We discuss the nuclear magnetic relaxation rate and the superfluid density with the use of the effective five-band model by Kuroki et al. [Phys. Rev. Lett. 101, 087004 (2008)] in Fe-based superconductors. We show that a fully-gapped anisotropic \pm s-wave superconductivity consistently explains experimental observations. In our phenomenological model, the gaps are assumed to be anisotropic on the electron-like \beta Fermi surfaces around the M point, where the maximum of the anisotropic gap is about four times larger than the minimum.Comment: 10 pages, 8 figures; Submitted versio

Profile of cervicobrachial neuralgia among rheumatology patients in Lomé, Togo

Objectives: To determine the frequency and the different clinical forms of cervicobrachial neuralgia in a rheumatological setting in Lomé, Togo.Design: This was a cross-sectional multicenter study conducted from January 2012 to December 2018 on the records of patients seen in the three rheumatology units in Lomé, Togo.Methods: Patients who reported for consultation purposely because of cervicobrachial neuralgia were included. Diagnosis of the various clinical forms of degenerative cervical spine disease was essentially clinical, whereas radiological imaging findings contributed to the diagnosis of spondylodiscitis and neoplastic disease.Results: Cervicobrachial neuralgia was the reason for the clinic visit in 143 (0.69%) out of the 14,346 patients examined over the eight year study period. These 143 patients comprising 84 women (58.74%) and 59 men (41.26%) had a mean age of 53.36±13.33 years. The average time to consultation was two years. Degenerative disease (138 cases,96.5%) was the most commonly observed pathology. It included the following clinical forms: cervical osteoarthritis (n=120; 83.91%), cervical myelopathy (n=13; 9.10%) and herniated disc (n=5; 3.49%). Disc degeneration in isolation (60.83%) was the main radiographic finding in patients with degenerative disease. Spondylodiscitis was probably due to tuberculosis in the four patients who had it and two of them were HIV- positive. Bone metastasis from prostate cancer was found in one case.Conclusion: Cervicobrachial neuralgia appears to be significant among rheumatology patients in Lomé. It predominantly affects adult women in professional activity. Althoughmainly dominated by degenerative pathology, its aetiologies can also be infectious as well as neoplastic, hence the relevance of modern imaging modalities. Key words: Cervicobrachial neuralgia, Osteoarthritis, Spondylodiscitis, Tumours, Sub-Saharan Afric

Polyarthrite rhumatoïde et hemoglobinopathie ss chez une femme de 61 ans

La survenue de la polyarthrite rhumatoïde (réputée moins fréquente en Afrique subsaharienne qu’en Occident) chez un malade atteint de drépanocytose (maladie génétique spécifique de la race noire) comporte des conséquences diagnostique thérapeutique et pronostique. Nous en rapportons un cas observé chez une femme de 61 ans dont la polyarthrite n’a été reconnu qu’au stade de carpite fusionnante bilatérale. La double coxopathie dont souffrait cette patiente relevait d’une nécrose d’allure aseptique des têtes fémorales. Le terrain et les différentes répercussions des deux affections ont rendu complexe la prise en charge de la patiente.   English title: Rheumatoïd arthritis and sickle cell disease in a 61-year – old woman The occurrence of rheumatoid arthritis (known to be less frequent in sub-Saharan Africa than in the West) in a patient with sickle cell disease (a specific genetic disease of the black race) has diagnostic, therapeutic and prognostic consequences. We report a case observed in a 61-year-old woman whose rheumatoid arthritis was only recognized at the stage of bilateral fusing carpitis. The bilateral hip involvement from which this patient was suffering was due to aseptic necrosis of the femoral heads. The terrain and the different repercussions of the two conditions made the patient management complex

Medication prior to rheumatology consultation in a Togolese Teaching Hospital

Objective: To determine the frequency and nature of the medication prior to specialized consultation in rheumatic patients. Design: This was a cross- sectional study of patients admitted for the first time for rheumatology consultation at CHU-SO in Lomé, Togo.Methods: The data relating to the medication prior to the consultation were collected by questioning. The diagnosis of the conditions covered by the consultation was based on clinical and para-clinical examinations. Results: Two hundred and eleven patients (151 women and 60 men) with a mean age of 49 years were included in the study. Forty-five patients (21%) were covered by health insurance because of their status as state employees, unlike the other 166 (79%) working in the informal sector. Spinal degenerative pathology (76%), knee osteoarthritis (20%) and tendinitis (10%) were the main diseases observed. One hundred and ninety- five patients(92%) were on medication prior to the rheumatology consultation. Non-steroidal anti- inflammatory drugs (118 cases, 75%) and analgesics (93 cases, 59%) were the most common therapeutic classes that were used. Self-medication was observed in 141 patients (67%) at all levels of education combined. Eighty- four of the 141patients(60%) have used street drugs, and 98 of them (70%) were oriented by word of mouth. General medical practitioners (25%) and medical assistants (19%) were the main prescribers before the rheumatology consultation. Epigastric pain (16 cases) was the main side effect observed. One hundred and forty- four patients (66%) had no idea of the risks of self-medication, added to lack of money by 122 (87%) patients and lack of knowledge of rheumatology by 67 (48%) patients. Conclusion: Self-medication, the frequency of which is known all over the world, is more notable in Africa and in rheumatic diseases where pain is the main symptom and its relief is one of the criteria for evaluating the effect of any therapy. Key words: Self-medication, Rheumatology, Togo, Afric