Structure and Phase Transitions of Alkyl Chains on Mica

We use molecular dynamics as a tool to understand the structure and phase transitions [Osman et. al. J. Phys. Chem. B 2000, 104, 4433; 2002, 106, 653] in alkylammonium micas. The consistent force field 91 is extended for accurate simulation of mica and related minerals. We investigate mica sheets with 12 octadecyltrimethylammonium (C18) ions or 12 dioctadecyldimethylammonium (2C18) ions, respectively, as single and layered structures at different temperatures with periodicity in the xy plane by NVT dynamics. The alkylammonium ions reside preferably above the cavities in the mica surface with an aluminum-rich boundary. The nitrogen atoms are 380 to 390 pm distant to the superficial silicon-aluminum plane. With increasing temperature, rearrangements of C18 ions on the mica surface are found, while 2C18 ions remain tethered due to geometric restraints. We present basal-plane spacings in the duplicate structures, tilt angles of the alkyl chains, and gauche-trans ratios to analyze the chain conformation. Also, the individual phase transitions of the two systems on heating are explained. Where experimental data are available, the agreement is very good. We propose a geometric parameter lamba for the saturation of the surface with alkyl chains, which determines the preferred self-assembly pattern, i.e., islands, intermediate, or continuous. Lambda also determines the tilt angles in continuous layers on mica or other surfaces. The thermal decomposition appears to be a Hofmann elimination with mica as a base-template.Comment: 45 pages with 6 tables and 5 figure

Bubble formation during the collision of a sessile drop with a meniscus

The impact of a sessile droplet with a moving meniscus, as encountered in processes such as dip-coating, generically leads to the entrapment of small air bubbles. Here we experimentally study this process of bubble formation by looking through the liquid using high-speed imaging. Our central finding is that the size of the entrapped bubble crucially depends on the location where coalescence between the drop and the moving meniscus is initiated: (i) at a finite height above the substrate, or (ii) exactly at the contact line. In the first case, we typically find bubble sizes of the order of a few microns, independent of the size and speed of the impacting drop. By contrast, the bubbles that are formed when coalescence starts at the contact line become increasingly large, as the size or the velocity of the impacting drop is increased. We show how these observations can be explained from a balance between the lubrication pressure in the air layer and the capillary pressure of the drop

Pre- and post-radiotherapy MRI results as a predictive model for response in laryngeal carcinoma

The purpose was to determine if pre-radiotherapy (RT) and/or post-radiotherapy magnetic resonance (MR) imaging can predict response in patients with laryngeal carcinoma treated with RT. Pre- and post-RT MR examinations of 80 patients were retrospectively reviewed and associated with regard to local control. Pre-RT MR imaging parameters such as tumor involvement of specific laryngeal anatomic subsites including laryngeal cartilages and post-RT changes, i.e., complete resolution of the tumor or focal mass/asymmetric obliteration of laryngeal tissue and signal pattern on T2-weighted images, were evaluated. Local control was defined as absence of a recurrence at the primary site for 2 years. Local control rates based on pretreatment MR findings were 73% for low pre- RT risk-profile and 29% for high pre- RT risk-profile patients (p=0.0001). Based on posttreatment MR findings, local control rates were 100% score 1, 64% score 2, and 4% score 3 (p< 0.0001). Using post-RT T2-weighted images, significant association was found between differences in signal pattern and local control: 77% hypointense, 54% isointense and 15% hyperintense lesions (p<0.001). Differences between means of delay of post-MRI examination were significantly associated with regard to local control (p=0.003); recurrent tumors followed 5 months after RT were more easily detectable on MRI than recurrent tumors within 4 months after RT. Sensitivity, specificity, accuracy, negative and positive predictive values of post-RT score 3 were 96%, 76%, 83%, 98% and 66%. Pre- and post-RT MRI evaluation of the larynx can identify patients at high risk for developing local failure

Veranderingen in de TNM-classificatie van het hoofd-halscarcinoom

The TNM-classification of the UICC is used for staging malignant tumours worldwide. From 2003 the new revised sixth edition must be used. In comparison with the fifth edition there are some general and some head and neck carcinoma specific alterations. Some designations are introduced if sentinel lymph node procedure or immunohistochemistry or molecular methods have been used. In the revised version some definitions for advanced tumour stages at several head and neck sites are changed. In the new classification of the primary tumour the terms erosion and invasion of cartilage or bone are used. At most head and neck sites T4 is divided in T4a and T4b

Thymoma geassocieerde exfoliatieve dermatitis bij een kat

A 10-year-old male castrated European Shorthair was presented with signs of scaling, alopecia and pruritus. The dermatopathological examination demonstrated an interface dermatitis with a few apoptotic keratinocytes, a mural lymphocytic folliculitis and the absence of sebaceous glands. These skin changes are compatible with a paraneoplastic syndrome caused by a thymoma. A thoracic radiograph confirmed the presence of a mass in the cranial mediastinum. A sternal thoracotomy was performed. One large tumor and two smaller masses were removed. Histopathological examination of the masses revealed a lymphocyte-rich thymoma. Initially, the skin lesions improved significantly. A few weeks after surgery, there was a relapse of the exfoliative dermatitis, which regressed with a dexamethasone treatment. On the last follow-up consult, 6 months post-operatively, the cat was no longer administered any medication and only showed mild scaling and no pruritus

Predicting short-term disability progression in early multiple sclerosis: Added value of MRI parameters

Objective: Magnetic resonance imaging (MRI) and clinical parameters are associated with disease progression in multiple sclerosis (MS). The aim of this study was to investigate whether adding MRI parameters to a model with only clinical parameters could improve these associations. Methods: 89 patients (55 women) with recently diagnosed MS had clinical and MRI evaluation at baseline (time of diagnosis) and at follow-up after 2.2 years. Detailed clinical data were available, including disease type (relapse-onset or progressive-onset) and disability, as measured by the Expanded Disability Status Scale (EDSS). MRI parameters included Normalised Brain Volume (NBV) at baseline, percentage brain volume change (PBVC/year), T2- and T1-lesion loads and spinal cord abnormalities. Progression of disability (increase in EDSS of at least 1 point at follow-up) was the main outcome measure. For a model containing only clinical parameters, the added value of MRI parameters was tested using logistic regression. Results: PBVC/year and lesion loads at follow-up were significantly higher in the group with progression. Adding PBVC/year to a clinical model improved the model, indicating that MRI parameters added independent information (p<0.001). Conclusion: The rate of cerebral atrophy conveys added information for the progression of disability in patients with early MS, suggesting that clinical disability is determined by neurodegenerative changes as depicted by MRI

Critical Velocity in 3He-B Vibrating Wire Experiments as Analog of Vacuum Instability in a Slowly Oscillating Electric Field

The Lancaster experiments with a cylindrical wire moving in superfluid 3He-B are discussed, where the measured critical velocity of pair creation is much below the Landau critical velocity. The phenomenon is shown to be analogous to the instability of the electron-positron vacuum in an adiabatically alternating strong electric potential of both signs, where the positive- and negative-root levels cross and thus the instability treshold is twice less than in the conventional case of a single static potential well.Comment: RevTex file, 6 pages, 4 figure