Combinatorial molecular optimization of cement hydrates.

Despite its ubiquitous presence in the built environment, concrete's molecular-level properties are only recently being explored using experimental and simulation studies. Increasing societal concerns about concrete's environmental footprint have provided strong motivation to develop new concrete with greater specific stiffness or strength (for structures with less material). Herein, a combinatorial approach is described to optimize properties of cement hydrates. The method entails screening a computationally generated database of atomic structures of calcium-silicate-hydrate, the binding phase of concrete, against a set of three defect attributes: calcium-to-silicon ratio as compositional index and two correlation distances describing medium-range silicon-oxygen and calcium-oxygen environments. Although structural and mechanical properties correlate well with calcium-to-silicon ratio, the cross-correlation between all three defect attributes reveals an indentation modulus-to-hardness ratio extremum, analogous to identifying optimum network connectivity in glass rheology. We also comment on implications of the present findings for a novel route to optimize the nanoscale mechanical properties of cement hydrate.

Clustering in artificial categories: an equivalence analysis.

Category clustering is a robust finding in the free recall of familiar category members, but has rarely been studied with artificial categories. In the present study, college students learned artificial categories via stimulus-equivalence methodology. Arbitrary match-to-sample training with nonsense syllables established three interrelated conditional discriminations, and, for most subjects, unreinforced test trials revealed the emergent stimulus-control relations considered to be evidence of equivalence classes. Free-recall tests revealed evidence of significant within-class clustering both before and after equivalence testing, but was more pronounced after the equivalence tests. These findings confirm that classic phenomena like clustering in free recall can be studied with stimulus-equivalence methodology, thus allowing for experimental control over relevant variables.

Environmental enrichment committee: its role in program development.

The authors discuss the role of the Environmental Enrichment Committee in developing, implementing, assessing, and modifying a university animal enrichment program.

Group housing female guinea pigs.

Group housing guinea pigs can save space and money, while improving housing standards. The authors describe enclosure design, enrichments, and husbandry techniques that facilitate group housing female guinea pigs.

CHO feeding before prolonged exercise: effect of glycemic index on muscle glycogenolysis and exercise performance.

This study examined the effect of preexercise carbohydrate (CHO) ingestion on muscle CHO metabolism and performance during prolonged exercise. Six endurance-trained men performed three exercise trials on a cycle ergometer after ingesting either a high glycemic index (HGI), low glycemic index (LGI), or placebo (Con) meal 45 min before exercise. During each trial, subjects cycled at a workload corresponding to 70% peak oxygen uptake for 120 min, followed by a 15-min performance cycle where total work (kJ) was measured. Ingestion of HGI resulted in an elevated (P < 0.01) blood glucose concentration 15 min after ingestion, compared with LGI and Con, but there were no differences in the glycemic responses to the meals thereafter, despite plasma insulin concentration being higher (P < 0.01) throughout the rest period after ingestion of HGI compared with LGI and Con. Plasma free fatty acid concentrations were lower (P < 0.05) throughout exercise in HGI compared with LGI and Con. In addition, concentrations of this metabolite were lower (P < 0.05) during the first hour of exercise in LGI compared with Con. Despite these results, no differences were observed in either the rate of muscle glycogen utilization during submaximal exercise or work output during the performance cycle when the three trials were compared. These results demonstrate that preexercise CHO ingestion has no effect on muscle glycogen utilization or exercise performance, irrespective of the glycemic or insulinemic responses to the ingested meals.

Immediate complete dentures.

When dentists treat patients for immediate complete dentures, they assume responsibility not only for the clinical and laboratory techniques unique to immediate complete denture fabrication, but also the responsibility for informing their patients about their treatment options, instructing their patients in the care of their oral tissues and dentures, and for continuing maintenance of the immediate dentures. Immediate dentures can be a traumatic introduction to complete dentures if patients are not informed fully about the complexity of the clinical and laboratory procedures, the need for immediate denture maintenance, and the costs associated with immediate denture treatment. The importance of 8 to 12 months of continuing care for immediate denture patients must be explained to patients and the dangers of neglecting continuing care must be emphasized.

Squamous cell carcinoma of the external auditory canal. Therapeutic prognosis based on a proposed staging system.

OBJECTIVE: To determine the adequacy of the proposed TNM staging system and evaluate the therapeutic modalities used at our institution in an attempt to synthesize guidelines for therapy of primary squamous cell carcinoma (SCC) of the temporal bone. DESIGN: Case series of 22 patients with previously untreated or residual SCC of the temporal bone treated between 1970 and 1990. Mean follow-up of the surviving patients was 124.5 months (range, 46 to 210 months). SETTING: University of Texas M. D. Anderson Cancer Center, Houston, an ambulatory and hospitalized care referral center. PATIENTS: The hospital charts of 41 patients with carcinoma of the temporal bone seen between 1970 and 1990 were retrospectively reviewed. Twenty-two of these patients had previously untreated or residual SCC of the external auditory canal and were chosen for this study. Information was collected regarding symptoms, tumor location, treatment methods, pathologic diagnosis, and patient outcomes. MAIN OUTCOME MEASURE: Accuracy of proposed staging system in predicting 5-year survival. Effect of surgery alone, radiotherapy alone, and surgery combined with radiotherapy on survival. RESULTS: Using the Pittsburgh staging system, the conditions of eight patients (36%) were staged at T1, four (18%) were staged at T2, six (27%) were staged at T3, and four (18%) were staged at T4. (The 19 patients with either recurrent disease or non-SCC were also treated, but their conditions were not staged). Statistical validation is impossible owing to the small sample sizes. Combination therapy with surgery and radiotherapy provided a higher 5-year survival rate than surgery or radiotherapy alone. Extrapolation of our data confirms that a staging system is useful in planning therapy. Surgical resection followed by radiotherapy is the preferred treatment for SCCs of the external auditory canal.

Paragangliomas of the temporal bone.

Recent advances in diagnosis and surgical therapy of glomus tumors of the temporal bone have been made. These advances make it possible for surgeons to benefit patients affected by this locally aggressive and morbid tumor. More sensitive diagnostic modalities and a physician alertness make early surgical cure a possibility. Careful planning and observation of basic surgical principles help to minimize morbidity and improve functional results.

Bladder compliance in meningomyelocele children.

The 2 components of detrusor compliance were analyzed in 32 children with myelomeningocele and compared to compliance in 15 age-matched controls with nonneuropathic enuresis. In myelomeningocele initial compliance was variable, whereas terminal compliance was relatively constant. Low terminal compliance corresponded with vesicoureteral reflux, deterioration of upper tract morphology and diminished renal function.