Competition of Mesoscales and Crossover to Tricriticality in Polymer Solutions

We show that the approach to asymptotic fluctuation-induced critical behavior in polymer solutions is governed by a competition between a correlation length diverging at the critical point and an additional mesoscopic length-scale, the radius of gyration. Accurate light-scattering experiments on polystyrene solutions in cyclohexane with polymer molecular weights ranging from 200,000 up to 11.4 million clearly demonstrate a crossover between two universal regimes: a regime with Ising asymptotic critical behavior, where the correlation length prevails, and a regime with tricritical theta-point behavior determined by a mesoscopic polymer-chain length.Comment: 4 pages in RevTeX with 4 figure

Probing structural relaxation in complex fluids by critical fluctuations

Complex fluids, such as polymer solutions and blends, colloids and gels, are of growing interest in fundamental and applied soft-condensed-matter science. A common feature of all such systems is the presence of a mesoscopic structural length scale intermediate between atomic and macroscopic scales. This mesoscopic structure of complex fluids is often fragile and sensitive to external perturbations. Complex fluids are frequently viscoelastic (showing a combination of viscous and elastic behaviour) with their dynamic response depending on the time and length scales. Recently, non-invasive methods to infer the rheological response of complex fluids have gained popularity through the technique of microrheology, where the diffusion of probe spheres in a viscoelastic fluid is monitored with the aid of light scattering or microscopy. Here we propose an alternative to traditional microrheology that does not require doping of probe particles in the fluid (which can sometimes drastically alter the molecular environment). Instead, our proposed method makes use of the phenomenon of "avoided crossing" between modes associated with the structural relaxation and critical fluctuations that are spontaneously generated in the system.Comment: 4 pages, 4 figure

Early postoperative MRI overestimates residual tumour after resection of gliomas with no or minimal enhancement

Standards for residual tumour measurement after resection of gliomas with no or minimal enhancement have not yet been established. In this study residual volumes on early and late postoperative T2-/FLAIR-weighted MRI are compared. A retrospective cohort included 58 consecutive glioma patients with no or minimal preoperative gadolinium enhancement. Inclusion criteria were first-time resection between 2007 and 2009 with a T2-/FLAIR-based target volume and availability of preoperative, early (<48 h) and late (1-7 months) postoperative MRI. The volumes of non-enhancing T2/FLAIR tissue and diffusion restriction areas were measured. Residual tumour volumes were 22% smaller on late postoperative compared with early postoperative T2-weighted MRI and 49% smaller for FLAIR-weighted imaging. Postoperative restricted diffusion volume correlated with the difference between early and late postoperative FLAIR volumes and with the difference between T2 and FLAIR volumes on early postoperative MRI. We observed a systematic and substantial overestimation of residual non-enhancing volume on MRI within 48 h of resection compared with months postoperatively, in particular for FLAIR imaging. Resection-induced ischaemia contributes to this overestimation, as may other operative effects. This indicates that early postoperative MRI is less reliable to determine the extent of non-enhancing residual glioma and restricted diffusion volumes are imperativ

Facial emotion recognition deficits and alexithymia in borderline, narcissistic, and histrionic personality disorders.

Previous studies that aimed to support emotion recognition deficits and alexithymia in B cluster personality disorders have mainly focused on borderline personality disorder (BPD), and resulted in mixed findings. In our study we examine emotion recognition and alexithymia in patients with histrionic (HPD), narcissistic (NPD) and borderline (BPD) personality disorders compared to each other and healthy controls. Furthermore, the possibility is investigated that it is not the type of PD but the severity of psychopathology which predicts the severity of emotion recognition deficits and alexithymia. Patients with HPD, NPD, BPD and healthy controls (N=20 for each group) were examined by using the Ekman 60 Faces Test (FEEST) and the Toronto Alexithymia Scale (TAS-20). To measure the extent and severity of psychopathology, the Symptom-Checklist-90 Revised (SCL-90-R) was used. Patient groups performed significantly worse compared to healthy controls on the Ekman test and TAS-20, while we found no significant differences among patient groups in emotion recognition and alexithymia. Furthermore, higher scores on the SCL-90-R predicted poorer emotion recognition performance and higher alexithymic features. The empirical data supports the conclusion that the severity of psychopathology plays an important role in predicting emotion recognition deficits and alexithymia in borderline, narcissistic, and histrionic personality disorders