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At least 19 recordsLinked to original sources
PubMed1977

[Hard-x-ray therapy. The position between orthovolt- and ultra hard ray therapy (author's transl)].

The special position of "hard-ray therapy" (RT 305, 300 kV) between the orthovolt-therapy and the ultra-hard-ray therapy is described in physical respect and clinical practicability. In comparison with the orthovolt-therapy there is an advantage in better skin tolerance, the absence of bone shadows and the possibility to increase the depth-dose up to 50%. The main indications are given in the intermediate therapy and the short distance therapy of greater tumors. The palliative deep therapy is administered under better conditions as with the conventional x-ray irradiation.

Bone Neoplasms↗
PubMed1979

[Effect of long-term moderately hard and hard physical work on the psychomotor efficiency and mental work capacity (II.)].

23 women, aged 19--24, of average physical efficiency, were examined. The following aspects were taken into account: an influence of long-lasting cyclic physical work on bicycle ergometer on the results obtained during the visual and auditory reaction time, the task performed with different speed using the test of visual and motorial coordination and Piórkowski's Test, as well as work efficiency in Pauli's test and learning and reproduction of nonsensical syllables. Long-lasting physical work resulted in a significant prolongation of the visual reaction time and increased number of mistakes in case of a task performed with maximum speed using the test of visual and motorial coordination. Negative but weak effects of physical effort were observed in the results of auditory reaction time and tasks checking the mental work efficiency. In the initial stage of the experiment (the early part) in some tasks a positive effect of physical effort was observed.

Adult↗
PubMed1978

Direct measurement of myocadial hardness.

Myocardial hardness, defined as resistance to a pitting force, was measured on several sites of the myocardium in 20 anesthetized dogs. The durometer used for hardness measurements consisted of an indentor, 4 mm in diameter, pressed perpendicularly on the myocardium by a calibrated spring (elastic modulus 325 N/m). Hardness changes during the cardiac cycle caused movement of the indentor which interrupted a light beam falling on a photoresistance. Changes in illumination of the photoresistance resulted in resistance changes, which were recorded using a Wheatstone bridge and a DC amplifier. Hardness was expressed in mm of spring shortenings. Balanced in (zero hardness), the indentor protruded 7.2 mm beyond the foot. Thus hardness adequate to press the indentor level with the foot defined as 7.2 mm. The left ventricular pressure (LVP) rise followed slightly the hardness rise (from 29.5 +/- 3.6 msec--mean +/- SEM--for the basal area at the right ventricle to 35.8 +/- 5.9 msec for the basal area of the left ventricle. Apical areas were significantly harder in systole than corresponding basal areas and left ventricular areas had a significantly higher systolic hardness (SH) than corresponding right ventricular areas. Changes in LVP by transfusion bleeding caused almost proportional changes in SH. While using a constant pressure reservoir in left atrium and another in aorta, adrenaline caused a significant increase in SH, decrease in diastolic hardness (DH) and increase in hardness width (WH); calcium chloride caused a nonsignificant increase in SH and WH and a significant decrease in DH; practolol caused a nonsignificant decrease in SH and a significant increase in DH and decrease in WH. Ligation of 3--5 branches of the anterior descending coronary artery resulted in a significant increase in DH and reduction in the WH distally to the ligation during the first 11 min. The WH was significantly reduced as a function of time in both areas (healthy and infarcted) taken collectively. The WH was significantly higher over the healthy area than over the infarcted one at corresponding times.

Animals↗
PubMed1978

Biochemical significance of the hard and soft acids and bases principle.

The hard and soft acids and bases (HSAB) principle, which states that hard acids bind preferentially to hard bases and soft acids to soft bases, may serve to assess specific chemico-biological interactions. As living systems are composed mainly of "hard" elements, molecular events taking place within the cell are dominated by "hard-hard interactions". On this premise, it becomes likely that extraneous "soft" agents are particularly injurious to life. In the HSAB context a selected number of variegated phenomena are briefly discussed qualitatively; these include biocidal actions, heavy metal poisoning, chemical carcinogenesis, some enzymic reactions, and nucleic acid complexations. Although the HSAB principle cannot be used as a tool for mechanistic explanations of biochemical processes, it may provide clues to likely target molecules and the loci of action.

Acids↗
PubMed1976

Effects of film coatings on tablet hardness.

The effects of five conventional film-coating materials on tablet hardness were studied. Placebos showed apparently linear increases in hardness as coatings were applied. Completely coated samples exhibited hardness increases from 50 to 140%, with a corresponding 3% increase in tablet weight. Equations were derived relating hardness changes to the "breaking strength" of the film on the tablet. Findings indicate that the coatings exert their influence primarily along the diameter of the tablet in a direction perpendicular to an applied compressional force. Furthermore, the coating process itself did not alter core hardness since tablets from which the film could be stripped showed original values.

Cellulose↗
PubMed1978

Hardness increase induced by partial moisture loss in compressed tablets and its effect on in vitro dissolution.

The hardness increase induced by partial moisture loss in compressed tablets was studied. Several factors such as the type and percentage of the excipient, the water solubility and hygroscopicity of the excipient or drug, and the influence of frequently used binders were investigated. The results indicate that the tablets increased in hardness by the recrystallization of the soluble excipient or the soluble drug in the void spaces This recrystallization occurred because of the moisture loss after expulsion of the solution of the excipient or drug in the void spaces on compression. The large increase in hardness induced by the partial moisture loss did not decrease in vitro dissolution appreciably. This result was clearly different from the hardness increase caused by higher compression loads in the absence of a moisture-induced effect, which showed a decrease in the in vitro dissolution as the hardness was increased.

Crystallization↗
PubMed1978

Hard contact lens wear as an environmental risk in keratoconus.

We studied 162 keratoconus patients in an attempt to clarify the role of hard contact lens wear in the development of keratoconus. Forty-three (26.5%) of these 162 patients developed keratoconus while wearing hard contact lenses. In a group of 1,248 controls who were fitted for soft contact lenses and observed by us from one year to six years, only one patient developed keratoconus. We demonstrated a circumstantial association between hard contact lens wear and the development of keratoconus, but no cause-effect relationship can be drawn from the existing data. However, we concluded that hard contact lenses do not retard or halt progression of the cone. Hard contact lens wear could not be ruled out as the specific environmental risk factor triggering keratoconus in 26.5% of the patients. If we identify the genetic risk present in this subpopulation, eliminating environmental risks would be an effective means of preventing keratoconus in those predisposed individuals.

Contact Lenses↗
PubMed1979

Conductivity and hardness changes in aged compacts.

Batches of sodium, potassium, and ammonium chloride tablets containing no excipients and spray-dried lactose tablets containing 0.5% magnesium stearate were stored at 20 and 76% relative humidity. Electrical resistance and hardness measurements were made within 1 hr after compression and at intervals during a 45-day period. Hardness values of sodium, potassium, and ammonium chloride tablets stored at 20% relative humidity increased from 70 to 200% at 45 days, while conductances decreased 10-fold. Tablets stored at 76% relative humidity showed no increases or slight decreases in hardness with slight increases in conductance. Lactose tablets decreased slightly in hardness with corresponding increases in conductance.

Ammonium Chloride↗
PubMed1975

Effects of hardness on the disintegration time and the dissolution rate of uncoated caffeine tablets.

The effects of hardness on disintegration and dissolution characteristics of uncoated caffeine tablets made at eight different pressure levels were studied. The disintegration times were determined using the J.P. VIII procedure with disks and the dissolution rate measurements were performed with the U.S.P.XVIII procedure (U.S.P. method) and the J.P. VIII disintegration test apparatus (J.P. method). A good correlation between the hardness and the disintegration times was obtained. The dissolution rate constants were determined from the equation of Noyes & Whitney (1897) and a good correlation between the hardness and the dissolution rate constants was obtained. The hardness governed the dissolution over all the stages from tablet to the smallest particles after the breakage by disintegration. The dissolution rates of the J.P. method were greater than those of the U.S.P. method.

Caffeine↗
PubMed1977

[The determination of mechanical properties of hard tissue surfaces in microareas by means of mechano-electrical methods].

The resistance of surfaces of hard tissue against chemical attacks e.g. acids can be measured with high spacial specifity by electro-mechanical registration of surface topograms. Apart from this property of hard substance, important in connection with the development of caries, the sample principle of measurement can be used in vitro on dental surfaces to obtain other important measurements. Examples are given to show how the hardness is determined by the summation of elastic and plastic properties. It is shown how far during the usual measurements for hardness of impressions the duration of the process and the time elapsed before measurement can influence the results.

Acids↗
PubMed1976

Comparative evaluation of tablet lubricants: effect of application method on tablet hardness and ejectability after compression.

The effect of four lubricants (stearic acid, magnesium stearate, calcium stearate, and talc) on the ejectability and hardness of statically compressed tablets of a lactose granulation was examined. Two methods of application of these lubricants, incorporation into the granulation and mixing with the granulation, were compared. In both methods, the energy consumption curves during ejection and the hardness curves with lubricant concentration were similar and showed complicated behavior at a lower concentration. The mixing method gave better results for ejectability and hardness than the incorporation method.

Drug Compounding↗
PubMed1977

Hardness testing of some fissure-sealing materials.

The mechanical properties of fissure-sealing materials are of significant importance for their durability, i.e. their wear resistance. One of the methods of evaluating a material's resistance to attrition is to apply a hardness test. In the present investigation, the surface hardness of some fissure-sealing materials was tested. Sealants made from diluted composite materials and with inclusion of inorganic filler particles appeared to have a considerable higher surface hardness than the other sealing materials tested.

Composite Resins↗
PubMed1979

Wear of composites by abrasives of varying hardness.

The relationship between the wear of three composite resins and the hardness of the abrasive was studied by a two-body abrasion test. The wear rates of the composites increased linearly with abrasive hardness from 530 to 2080 KHN. Measurement of the slope of the wear rate versus abrasive hardness over this range provided a sensitive method for ranking the composites.

Aluminum Oxide↗
PubMed1977

Structure and hardness of four types of amalgam.

Three non-gamma2 and one conventional amalgams were compared for their structure and hardness. The Ag-Cu dispersants hardened the amalgam by generating hard Cu-Sn halos and diminishing the gamma2 phase. The Ag-Sn-Cu-In single composition alloy produced the hardest amalgam by its high hardness and the Cu-Sn reaction phase scattered as minute granules.

Chemical Phenomena↗