Why many polymers are so fragile: A new perspective.

Many polymers exhibit much steeper temperature dependence of their structural relaxation time (higher fragility) than liquids of small molecules, and the mechanism of this unusually high fragility in polymers remains a puzzle. To reveal additional hints for understanding the underlying mechanism, we analyzed correlation of many properties of polymers to their fragility on example of model polymer polystyrene with various molecular weights (MWs). We demonstrate that these correlations work for short chains (oligomers), but fail progressively with increase in MW. Our surprising discovery is that the steepness of the temperature dependence (fragility) of the viscosity that is determined by chain relaxation follows the correlations at all molecular weights. These results suggest that the molecular level relaxation still follows the behavior usual for small molecules even in polymers, and its fragility (chain fragility) falls in the range usual for molecular liquids. It is the segmental relaxation that has this unusually high fragility. We speculate that many polymers cannot reach an ergodic state on the time scale of segmental dynamics due to chain connectivity and rigidity. This leads to sharper decrease in accessible configurational entropy upon cooling and results in steeper temperature dependence of segmental relaxation. The proposed scenario provides a new important insight into the specifics of polymer dynamics: the role of ergodicity time and length scale. At the end, we suggest that a similar scenario can be applicable also to other molecular systems with slow intra-molecular degrees of freedom and to chemically complex systems where the time scale of chemical fluctuations can be longer than the time scale of structural relaxation.

Following the dynamics of matter with femtosecond precision using the X-ray streaking method.

X-ray Free Electron Lasers (FELs) can produce extremely intense and very short pulses, down to below 10 femtoseconds (fs). Among the key applications are ultrafast time-resolved studies of dynamics of matter by observing responses to fast excitation pulses in a pump-probe manner. Detectors with sufficient time resolution for observing these processes are not available. Therefore, such experiments typically measure a sample's full dynamics by repeating multiple pump-probe cycles at different delay times. This conventional method assumes that the sample returns to an identical or very similar state after each cycle. Here we describe a novel approach that can provide a time trace of responses following a single excitation pulse, jitter-free, with fs timing precision. We demonstrate, in an X-ray diffraction experiment, how it can be applied to the investigation of ultrafast irreversible processes.

The linac coherent light source single particle imaging road map.

Intense femtosecond x-ray pulses from free-electron laser sources allow the imaging of individual particles in a single shot. Early experiments at the Linac Coherent Light Source (LCLS) have led to rapid progress in the field and, so far, coherent diffractive images have been recorded from biological specimens, aerosols, and quantum systems with a few-tens-of-nanometers resolution. In March 2014, LCLS held a workshop to discuss the scientific and technical challenges for reaching the ultimate goal of atomic resolution with single-shot coherent diffractive imaging. This paper summarizes the workshop findings and presents the roadmap toward reaching atomic resolution, 3D imaging at free-electron laser sources.

Role of disorder in the thermodynamics and atomic dynamics of glasses.

We measured the density of vibrational states (DOS) and the specific heat of various glassy and crystalline polymorphs of SiO2. The typical (ambient) glass shows a well-known excess of specific heat relative to the typical crystal (α-quartz). This, however, holds when comparing a lower-density glass to a higher-density crystal. For glassy and crystalline polymorphs with matched densities, the DOS of the glass appears as the smoothed counterpart of the DOS of the corresponding crystal; it reveals the same number of the excess states relative to the Debye model, the same number of all states in the low-energy region, and it provides the same specific heat. This shows that glasses have higher specific heat than crystals not due to disorder, but because the typical glass has lower density than the typical crystal.

[Post-infectious irritable bowel syndrome]. / Sindrome dell'Intestino Irritabile Post-infettivo.

Acute infectious gastroenteritis is the strongest known risk factor for the development of irritable bowel syndrome (IBS), one of the most common functional gastrointestinal disorders. The knowledge about the incidence and prevalence of post-infectious IBS (PI-IBS) in the general population is still limited. Risk factors have been identified in the development of PI-IBS. These include the virulence of the pathogen, younger age, female sex, the long duration of the initial illness and the presence of psychological disturbances. Histopathologic data demonstrate a low-grade mucosal inflammation in a subset of patients with IBS. Furthermore, a change in intestinal microflora could also be involved although confirmatory studies are required. The use of probiotics or non absorbable antibiotics during the acute infective episode could play a preventive role. Nonetheless, the discovery that an infective episode may trigger the development of IBS has not substantially changed the clinical management of this subset of patients compared to the classical (non infective) form of IBS. Future studies aimed at identifying specific therapies are waited.

Vibrational dynamics of permanently densified GeO2 glasses: densification-induced changes in the boson peak.

Vitreous GeO(2), one of the main prototypes of strong glasses, was densified at several pressures up to 6 GPa, achieving more than 20% of densification. The density dependence of the vibrational density of states and of the low temperature properties of these glasses was investigated by means of inelastic neutron scattering and calorimetric measurements. With increasing density, both the boson peak and the bump in c(p)/T(3) versus T plot exhibit variations which are stronger than the elastic medium expectation. If one reduces the measured spectra to a common master curve, one finds that this is only possible for the densified samples; the first densification step has an additional effect, similar to other cases in the literature. Nevertheless, the existence of a master curve for the three densified samples proves that the total number of excess modes remains constant on further densification. The experimental data are discussed in the framework of different theoretical models.

Population structure of Macrobrachium australiense (Decapoda: Palaemonidae) in Western Queensland, Australia: the role of contemporary and historical processes.

Rivers of Western Queensland, Australia, represent a discontinuous and variable aquatic habitat for the freshwater fauna of the region. Rivers periodically fluctuate between being highly fragmented, with numerous disconnected waterholes and ephemeral channels, and being highly connected by a dominant system of anastomosing channels. We used mitochondrial sequences to investigate the genetic structure and inferred patterns of dispersal associated with this flow regime for the freshwater prawn, Macrobrachium australiense (Decapoda: Palaemonidae), sampling 28 localities throughout eight catchments. Based on a 505 base pair fragment of mitochondrial cytochrome c oxidase subunit I, we identified 98 haplotypes in a sample of 402 individuals. The haplotypes clustered into two main clades corresponding geographically to the major drainages: the Lake Eyre and Murray-Darling basins. Populations of M. australiense inhabiting the two basins appear to have diverged around 800,000 years ago (estimated sequence divergence of 1.6%). Analysis of population differentiation indicated contemporary high levels of genetic subdivision and restricted gene flow among populations within and among catchments. Phylogenetic analysis detected a series of historical range expansions in the region and we suggest that climate fluctuations during the Pleistocene have resulted in extensive floods that have promoted historical movements of aquatic organisms across catchment boundaries.

Left ventricular mass and cardiovascular morbidity in essential hypertension: the MAVI study.

OBJECTIVES: This study investigated the prognostic value of left ventricular (LV) mass at echocardiography in uncomplicated subjects with essential hypertension. BACKGROUND: Only a few single-center studies support the prognostic value of LV mass in uncomplicated hypertension. METHODS: The MAssa Ventricolare sinistra nell'Ipertensione study was a multicenter (45 centers) prospective study. The prespecified aim was to explore the prognostic value of LV mass in hypertension. Admission criteria included essential hypertension, no previous cardiovascular events, and age > or =50. There was central reading of echocardiographic tracings. Treatment was tailored to the single subject. RESULTS: Overall, 1,033 subjects (396 men) were followed for 0 to 4 years (median, 3 years). Mean age at entry was 60 years, and systolic/diastolic blood pressure was 154/92 mm Hg. The rate of cardiovascular events (x100 patient-years) was 1.3 in the group with normal LV mass and 3.2 in the group (28.5% of total sample) with LV mass > or =125 g/body surface area (p = 0.005). After adjustment for age (p < 0.01), diabetes (p < 0.01), cigarette smoking (p < 0.01) and serum creatinine (p = 0.03), LV hypertrophy was associated with an increased risk of events (RR [relative risk] 2.08; 95% CI [confidence interval]: 1.22 to 3.57). For each 39 g/m(2) (1 SD) increase in LV mass there was an independent 40% rise in the risk of major cardiovascular events (95% CI: 14 to 72; p = 0.0013). CONCLUSIONS: Our findings show a strong, continuous and independent relationship of LV mass to subsequent cardiovascular morbidity. This is the first study to extend such demonstration to a large nationwide multicenter sample of uncomplicated subjects with essential hypertension.

[Prognostic significance of normal exertion myocardial scintigraphy in asymptomatic subjects with abnormal ergometric test]. / Significato prognostico della scintigrafia miocardica da sforzo negativa in soggetti asintomatici con positività del test ergometrico.

AIM OF THE STUDY: ST-segment depression on exercise stress test (EST) is an independent predictor of future cardiac events. Nevertheless, in apparently healthy subjects without angina the occurrence of false positive results is frequent. Thallium myocardial imaging (TMI) may improve diagnostic and prognostic accuracy of EST. The aim of the present study was to assess the role of a normal exercise TMI for excluding a coronary artery disease in subjects with asymptomatic abnormal EST. METHODS: Subjects referred for TMI from 1/1980 to 5/1991 with an abnormal EST and without history of ischemic, congenital, or valvular heart disease or abnormal resting ECG were included into the study. 137 subjects (98 men, 39 women), mean age 53 +/- 8 yrs (range 37-74 yrs) were enrolled and followed-up for 6.4 yrs (range 3-13 yrs). Clinical indications for EST were: atypical chest pain in 56 (41%) cases, check-up in 52 (38%) cases, sport activity in 29 (19%) cases. All subjects had a maximal symptom-limited EST. Abnormal EST was defined by a horizontal or downsloping > or = 1 mm or upsloping > or = 1.5 mm ST-segment depression at 0.08 sec. from J-point, in at least 2 leads. EST was discontinued for fatigue in 129 (94%) cases, for ST-segment depression > or = 3 mm in 8 (6%) cases. None had chest pain during EST. All subjects selected for the study had normal TMI. Criteria for normal TMI were homogeneous Thallium uptake on postexercise images and a normal washout in the delayed images by qualitative analysis. Planar images were obtained in 118 (86%) cases, and tomographic SPECT images in 19 (14%). RESULTS: During the follow-up period no subject died for cardiac causes and only 9 subjects (1%/yr) had non fatal cardiac events: 4 (0.45%/yr) had a non fatal myocardial infarction (one subject had coronary angiography for postinfarction angina and subsequent 3 coronary bypass graft for multivessels disease), 2 subjects (0.2%/yr) became symptomatic for unstable angina (both had coronary angiography and subsequent PTCA for critical left main coronary artery stenosis) and 3 (0.34%/yr) developed stable angina (one had coronary angiography and subsequent bypass graft for a critical stenosis of left main coronary artery). Four further subjects died for non cardiac events. Comparing clinical data and TE results of subjects with and without coronary events, we found that some parameters were related to a higher incidence of cardiac events: hypertension (78% vs 31% respectively in subjects with and without cardiac events, p < 0.01), hypercholesterolemia (33% vs 4.7%, p < 0.01); > or = 2 conventional coronary risk factors (56% vs 17%, p < 0.02); and a slow regression of abnormal ST-segment depression during recovery (2.8 +/- 2 vs 1.5 +/- 1 min, p < 0.01). CONCLUSIONS: In conclusion, in subjects without typical chest pain and with abnormal asymptomatic EST, a normal exercise TMI identifies subjects with very low risk of future cardiac events (1%/yr). Our data suggest that subjects with abnormal asymptomatic EST should be routinely submitted to exercise TMI.

[Percutaneous transluminal coronary angioplasty for postinfarction residual ischemia: mid- and long-term results]. / Angioplastica coronarica transluminale percutanea per l'ischemia residua postinfartule: risultati a medio e lungo termine.

Aim of this study was to assess the long-term results of PTCA in patients with a recent myocardial infarction. The study population consisted of 244 consecutive patients who underwent a PTCA < or = 30 days after myocardial infarction either because of angina (116 patients), or because of provoked ischemia (62 patients), or in the absence of both (66 patients). "Simple" balloon angioplasty, without adjunctive devices, was performed. Most of the patients were seen at 1 year intervals at the outpatient clinic; otherwise information was gathered either from the family physician or by telephone. The following events were noted during a follow-up of 6-102 months (median 39 months): death, myocardial infarction, need for re-PTCA or surgical revascularization, recurrence of angina. Survival and event-free curves were calculated according to the method of Kaplan and Meier; statistical comparisons between the curves were obtained by the log-rank test. Periprocedural deaths, infarctions and surgical revascularizations are included in the actuarial curves. Differences were examined between patients with Q and non-Q wave infarctions, single vessel versus multivessel disease, left ventricular ejection fraction > or 50% versus < 50%. A clinical success was achieved in 85% of the procedures. Sixteen patients were lost at follow-up. Overall, within the first 30 days and during follow-up, 12 (4.9%) patients died, 19 (7.7%) suffered from myocardial infarction, 34 (13.9%) required re-PTCA or surgical revascularization, and 63 (25.8%) experienced angina again.(ABSTRACT TRUNCATED AT 250 WORDS)

Preoperative noninvasive coronary risk stratification in candidates for carotid endarterectomy.

BACKGROUND AND PURPOSE: Patients with symptomatic carotid stenosis who are candidates for carotid endarterectomy are at high short- and long-term risk of coronary events. To stratify patients at different risk of coronary events we investigated the usefulness of a noninvasive preoperative cardiological workup. METHODS: We studied 172 consecutive patients admitted to the Neurosurgical Department for symptomatic high-grade (70% to 99%) carotid stenosis (age, 42 to 74 years; mean, 57.8 years). Patients without history of coronary artery disease (CAD) and able to exercise were submitted to exercise electrocardiographic testing (EET) and, if abnormal, to exercise thallium myocardial imaging (TMI). Patients were classified into four groups: group 1, patients without CAD: no history of CAD, normal EET, or normal TMI in the presence of indeterminant EET (n = 93, 54%); group 2, patients with silent CAD: no history of CAD and concordant abnormal EET and TMI (n = 28, 16%); group 3, patients unable to exercise: no history of CAD and inability to perform adequate EET because of previous stroke or claudication (n = 29, 17%); and group 4, patients with known CAD: history of angina or myocardial infarction (MI) (n = 22; 13%). RESULTS: The four groups were comparable in regard to age, sex, and computed tomographic scan of the brain. The prevalence of stroke was higher in patients unable to exercise; hypercholesterolemia was more frequent in patients with known CAD. During the perioperative period (< or = 30 days after carotid endarterectomy), coronary events occurred in 3 patients (2%): fatal MI in 2 patients in group 4 and 1 patient in group 3. One hundred percent of patients were followed up for 6.2 years. Coronary events occurred in 23 of the 168 patients discharged from the hospital (13.7%); these were fatal in 11 (6.5%): 3 patients of group 1 (3%; sudden death in 2, fatal MI in 1), 8 patients of group 2 (29%; fatal MI in 5, unstable angina in 3), 8 patients of group 3 (28%; fatal MI in 4, nonfatal MI in 4), and 4 patients of group 4 (18%; fatal MI in 2, sudden death in 1, unstable angina in 1). Kaplan-Meier estimated curves of survival free from fatal and nonfatal coronary events were 97%, 51%, 49%, and 59%, respectively (P < .001, group 1 versus groups 2 and 3; P < .01, group 1 versus group 4). CONCLUSIONS: Among patients undergoing carotid endarterectomy, coronary events occurred twice as often as cerebral recurrences. A preoperative noninvasive cardiac investigation, including EET, can adequately identify groups of patients with diverse short- and long-term prognoses. In addition to patients with known CAD, those with silent CAD or who are unable to exercise represent, without the need of further investigation, groups at high risk of coronary events in long-term follow-up.

[Angiographic criteria in the diagnosis of hypertrophic cardiomyopathy]. / Criteri angiografici per la diagnosi di cardiomiopatia ipertrofica.

AIM: To evaluate the commonly adopted ventriculographic and coronarographic criteria of hypertrophic cardiomyopathy. POPULATION: Eleven cases of obstructive cardiomyopathy, 14 non-obstructive cardiomyopathies, 15 discrete subaortic stenoses, 10 valvular aortic stenoses, and 12 cases of hypertensive heart disease. The diagnosis had been arrived at by independent clinical, electrocardiographic, echocardiographic and haemodynamic methods, as appropriate. METHODS: Retrospective "blind" examination of biplane left ventriculography (30 degrees right anterior oblique, 60 degrees left anterior oblique, with cranial tilt) and coronary arteriography. We looked for the following features: subaortic chamber, asymmetric septal hypertrophy, peculiar left ventricular shape and systolic obliteration, systolic anterior movement of the mitral leaflets, systolic narrowing or compression of epicardial coronary arteries and septal perforators. RESULTS AND CONCLUSIONS: The following left ventricular features were significantly more frequent in hypertrophic obstructive cardiomyopathy, than in other forms: subaortic chamber, "banana" configuration in systole, subaortic conus, asymmetric hypertrophy, systolic anterior movement of the anterior leaflet of the mitral valve, and mitral regurgitation. A subaortic chamber was seen both in the obstructive form and in the discrete subaortic stenosis, but the cranial left anterior oblique projection could easily discriminate between them. If non-obstructive cardiomyopathy is defined with the current criteria (provocable pressure gradient of < or = 30 mm Hg in a patient with left ventricular hypertrophy of no known cause), no distinctive angiographic features can distinguish it from other forms of secondary left ventricular hypertrophy.