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PubMed2005

Testing models of parental investment strategy and offspring size in ants.

Parental investment strategies can be fixed or flexible. A fixed strategy predicts making all offspring a single 'optimal' size. Dynamic models predict flexible strategies with more than one optimal size of offspring. Patterns in the distribution of offspring sizes may thus reveal the investment strategy. Static strategies should produce normal distributions. Dynamic strategies should often result in non-normal distributions. Furthermore, variance in morphological traits should be positively correlated with the length of developmental time the traits are exposed to environmental influences. Finally, the type of deviation from normality (i.e., skewed left or right, or platykurtic) should be correlated with the average offspring size. To test the latter prediction, we used simulations to detect significant departures from normality and categorize distribution types. Data from three species of ants strongly support the predicted patterns for dynamic parental investment. Offspring size distributions are often significantly non-normal. Traits fixed earlier in development, such as head width, are less variable than final body weight. The type of distribution observed correlates with mean female dry weight. The overall support for a dynamic parental investment model has implications for life history theory. Predicted conflicts over parental effort, sex investment ratios, and reproductive skew in cooperative breeders follow from assumptions of static parental investment strategies and omnipresent resource limitations. By contrast, with flexible investment strategies such conflicts can be either absent or maladaptive.

Animals↗

PubMed2004

Neutron radiography inspection of investment castings.

Investment casting, also known as the lost wax process, is a manufacturing method employed to produce near net shape metal articles. Traditionally, investment casting has been used to produce structural titanium castings for aero-engine applications with wall thickness less than 1 in (2.54 cm). Recently, airframe manufacturers have been exploring the use of titanium investment casting to replace components traditionally produced from forgings. Use of titanium investment castings for these applications reduces weight, cost, lead time, and part count. Recently, the investment casting process has been selected to produce fracture critical structural titanium airframe components. These airframe components have pushed the traditional inspection techniques to their physical limits due to cross sections on the order of 3 in (7.6 cm). To overcome these inspection limitations, a process incorporating neutron radiography (n-ray) has been developed. In this process, the facecoat of the investment casting mold material contains a cocalcined mixture of yttrium oxide and gadolinium oxide. The presence of the gadolinium oxide, allows for neutron radiographic imaging (and eventual removal and repair) of mold facecoat inclusions that remain within these thick cross sectional castings. Probability of detection (POD) studies have shown a 3 x improvement of detecting a 0.050 x 0.007 in2 (1.270 x 0.178 mm2) inclusion of this cocalcined material using n-ray techniques when compared to the POD using traditional X-ray techniques. Further, it has been shown that this n-ray compatible mold facecoat material produces titanium castings of equal metallurgical quality when compared to the traditional materials. Since investment castings can be very large and heavy, the neutron radiography facilities at the University of California, Davis McClellan Nuclear Radiation Center (UCD/MNRC) were used to develop the inspection techniques. The UCD/MNRC has very unique facilities that can handle large parts up to 39 ft (12 m) in length and 13 ft (4 m) high weighing up to 5000 lbs (2300 kg). These handling systems are robotically driven. The neutron radiographic system consists of a highly thermalized neutron beam. The neutron beam has an intensity of 5.6 x 10(6) n/cm2 s, with a L/D = 200 at a power of 2 MW. A divergent beam collimator is used which provides a beam of approximately 22 in (56 cm) in diameter at the film plane. A vacuum cassette with a gadolinium vapor deposited screen is used to collect the image. Exposure times can be as short as 3 min, or up to 30 min.

Journal Article↗

PubMed1999

Variable investment, the Continuous Prisoner's Dilemma, and the origin of cooperation.

Cooperation is fundamental to many biological systems. A common metaphor for studying the evolution of cooperation is the Prisoner's Dilemma, a game with two strategies: cooperate or defect. However, cooperation is rare all or nothing, and its evolution probably involves the gradual extension of initially modest degrees of assistance. The inability of the Prisoner's Dilemma to capture this basic aspect limits its use for understanding the evolutionary origins of cooperation. Here we consider a framework for cooperation based on the concept of investment: an act which is costly, but which benefits other individuals, where the cost and benefit depend on the level of investment made. In the resulting Continuous Prisoner's Dilemma the essential problem of cooperation remains: in the absence of any additional structure non-zero levels of investment cannot evolve. However, if investments are considered in a spatially structured context, selfish individuals who make arbitrarily low investments can be invaded by higher-investing mutants. This results in the mean level of investment evolving to significant levels, where it is maintained indefinitely. This approach provides a natural solution to the fundamental problem of how cooperation gradually increases from a non-cooperative state.

Biological Evolution↗

PubMed2002

Intrafamilial conflict and parental investment: a synthesis.

We outline and develop current theory on how inherent genetic conflicts of interest between the various family members can affect the flow of parental investment from parents to offspring, and discuss the problems for empirical testing that this generates. The parental investment pattern realized in nature reflects the simultaneous resolution of all the conflicts between the family players. This depends on the genetic mechanism, the mating system and reproductive constraints, on whether extra demand by progeny affects current or future sibs, and particularly on the behavioural mechanisms underlying demand (begging or solicitation) and supply (provision of parental investment by parents). The direction of deviation from the optimal parental investment for the parent(s) depends on the slope of what we term the 'effect of supply on demand', the mechanism that determines how changes in food supply affect begging levels. If increasing food increases begging (positive slope), less parental investment is supplied than the parental optimum and if increasing food decreases begging (negative slope), more parental investment is supplied. The magnitude of deviation depends on both the 'effect of supply on demand' and on the 'effect of demand on supply' (the mechanism determining how changes in begging affect food supply, which always has a positive slope). We conclude that it will often be impossible to deduce the extent of underlying conflict by establishing the amount of parental investment given relative to the ideal optimum for the parent. Some possible directions for future research are discussed.

Animals↗

PubMed1992

Relationships among marital investment, marital satisfaction, and marital commitment in domestically victimized and nonvictimized wives.

The present investigation examined the association between marital investment, marital satisfaction, and commitment to marriage among physically abused women. We applied an investment model and a social learning model to understanding victimized wives' satisfaction and commitment to stay married. Thirty wives who reported physical abuse and 58 nonabused wives completed measures of marital stability, investment in marital problem solving, and dyadic adjustment. Investment in marital problem solving was assessed by having subjects indicate how much energy that they have put into solving 34 common marital problems and whether their efforts were successful or not successful. Consistent with a social learning model but counter to an investment perspective, correlational and multiple regression analyses for each group revealed that failed investment was significantly related to lower, not greater, commitment. Group differences also emerged. Whereas nonabused wives' commitment was related to their dyadic adjustment abused wives' commitment was related to their level of failed investment. Results are consistent with the notion that women may remain in abusive relationships because of psychological entrapment.

Adult↗

PubMed2004

[The expression of nm23-H1 in the investing papilloma and it's cancerated tissue of nasal cavity and parasinuses].

OBJECTIVE: To investigate the role of the nm23-H1 protein in the development of investing papilloma and it's cancerated tissue in nasal cavity and parasinuses. METHOD: The expression of nm23-H1 protein was measured by immunohistochemistry in twenty-five cases with investing papilloma and twenty-one cases with cancerated investing papilloma in nasal cavity and parasinuses and fourteen cases with chronic sinusitis. RESULT: The expression of nm23-H1 in the investing papilloma was higher than that in cancerated investing papilloma tissue, the positive rate was 72% and 42% respectively in the two groups, P < 0.05. The expression of nm23-H1 in the investing papilloma was higher than in the chronic sinusitis, the positive rate of the latter was 14.3%, P < 0.05. CONCLUSION: The lower expression the nm23-H1 protein in the cancerated tissue of investing papilloma was related to the infiltration and canceration.

Adult↗

PubMed1980

Effect of investment on casting high-fusing alloys.

A definite interaction in castability was found between the three different phosphate-bonded investments and four different alloys tested in this study. 1. Casting completeness of all alloys, as measured by the length of test specimens, was affected by the investment. The high-gold content alloy, SMG II, yielded the most complete castings of all combinations teted when invested with Ceramigold. Of the nonprecious alloys, Biobond CB combined with Ceramigold II resulted in the longest samples. 2. The surface quality of Jelbon and SMG II castings was good, regardless of the investment used. Wiron S and Biobond CB varied in surface quality with different investments, Ceramigold II giving the smoothest castings. 3. All alloys, especially the nonprecious ones, should be tested for compatability with different investments before asserting their qualities or lack of qualities for clinical use.

Dental Alloys↗

PubMed1980

Tooth movement and dimensional change of denture base materials using two investment methods.

This in vitro investigation evaluated methods of investing a maxillary denture (1) by using a silicone rubber and gypsum base covering all the artificial teeth and (2) by following the generally accepted procedure of investing in a total gypsum environment. The amount of vertical opening found in dentures processed with silicone investment was approximately the same as for those processed with the all-gypsum technique, the horizontal movement of the teeth was more lingual in the silicone investment technique. Comparing the weight of the residual impression between the denture base of acrylic resin and the master die showed no significant difference between the silicone investments and the gypsum technique. The relined denture base provided a more accurate fit than a heat-cured denture processed in both types of investment, silicone and all-gypsum. Finally, a special device was developed that permitted tooth movement in processed dentures to be measured simply and accurately.

Calcium Sulfate↗

PubMed1989

Porosity determination of cast investment by a wax-infiltration technique.

A reproducible method of determining the porosity (pore volume) of cast investment materials is described. This procedure, requiring no highly specialized equipment, involved the infiltration of a test sample with paraffin wax and the weighing of the wax-infiltrated sample in both air and water. Pore-volume wax is then extracted with chloroform and the sample reweighed. The difference in weight is used to calculate the porosity of the investment material. Pore-volume data thus obtained are comparable to those resulting from standard techniques and far more sophisticated (and expensive) instrumentation. The porosities of hand-mixed samples of gypsum-bonded, phosphate-bonded and silica-bonded investments were 53.9 per cent, 36.9 per cent and 31.4 per cent and those of the vacuum-mixed samples were 52.5 per cent, 31.3 per cent and 26.9 per cent, respectively. The results show that gypsum-bonded investments were more porous than phosphate-bonded investments while silica-bonded investments were the least porous. Hand-mixed samples appeared to have greater porosity than vacuum-mixed samples.

Calcium Sulfate↗

PubMed2005

Novel method for titanium crown casting using a combination of wax patterns fabricated by a CAD/CAM system and a non-expanded investment.

OBJECTIVES: For titanium casting, most commercial investments for titanium recommend casting at a low mold temperature to reduce oxidation. However, the thermal expansion values of the molds at low casting temperatures may be insufficient. The purpose of the current study was to investigate the possibility of obtaining accurate titanium crown casts using wax pattern fabricated by a CAD/CAM system with a non-expanded mold. METHODS: Three types of experimental magnesia-based investments (A, B and C) were made and their properties were evaluated for dental use. Two kinds of wax patterns for full-coverage coping crowns (S-0: cement space of 0 microm; S-20: cement space of 20 microm) were fabricated using a commercial CAD/CAM system. A traditional method (TM) using inlay wax was performed for comparison. The investment for titanium casting was decided from the fundamental data of experimental investments. Titanium crowns were replaced on the stone die and the thickness of the cement layer was evaluated. RESULTS: There were no significant differences for the setting time and setting expansion among the experimental investments, but the aluminous cement content played a role in hardening and contracting the mold. The fit of the titanium crowns differed significantly between the TM and the CAD/CAM system. The ranges of thickness obtained from the TM, S-0 and S-20 were 20.78-357.88 microm, 25.12-107.46 microm and 17.84-58.92 microm, respectively. SIGNIFICANCE: High quality titanium crown casting was obtained using a combination of wax patterns fabricated by a CAD/CAM system and a non-expanded MgO-based investment.

Analysis of Variance↗

PubMed1999

Comparision of diametral tensile strength of microwave and oven-dried investment materials.

STATEMENT OF PROBLEM: Microwave drying technique for investment materials is believed to be timesaving by accelerating the elimination of free water content. PURPOSE: This study compared the diametral tensile strength of 4 investment materials used in removable partial denture framework fabrication. The investment materials were subjected to microwave and conventional oven drying at different time intervals. MATERIAL AND METHODS: Type III partial denture casting investments (Wirovest, Wiroplus, Biosint, PH2) were tested. A total of 160 specimens were prepared in cylindrical form at a height of 40 mm and a diameter of 20 mm, in accordance with the manufacturers' recommendations. Forty specimens were prepared from each product; 20 specimens were dried at 230 degrees C for 1 hour in an electric furnace, the other 20 were dried in a microwave oven for 10 minutes at 600 W. The dried specimens were tested at 2- and 4-hour intervals in diametral compression at a crosshead speed of 0. 5 cm/min. RESULTS: The microwave drying technique resulted in greater diametral tensile strength values for all investment materials. CONCLUSION: Within the limitations of this study, microwave drying of type III dental investment materials at 600 W for 10 minutes was, apart from strengthening the material, timesaving for the dental laboratory.

Analysis of Variance↗

PubMed1999

Marginal gap of crowns made with a phosphate-bonded investment and accelerated casting method.

STATEMENT OF PROBLEM: Numerous materials and methods have been used for complete crown fabrication. Conventional investing and casting procedures for phosphate-bonded investments require a 2- to 4-hour process before completion. Accelerated laboratory techniques have been used, but may not result in castings with equal marginal accuracy. PURPOSE: This study measured the marginal gap and determined the clinical acceptability of single castings invested in a phosphate-bonded investment with the use of conventional and accelerated methods. MATERIAL AND METHODS: Forty-four individual stone casts were poured from impressions made from a master die. Conventional and accelerated methods of investing and casting were followed in the fabrication of 44 single-unit castings. Twenty-two casts were used in each of the 2 groups. Each casting and its respective stone die were examined with a microscope at 4 predetermined sites. Perpendicular and 25-degree tilted measurements of marginal gap were documented for each. Evidence of marginal gap was then evaluated by t test. RESULTS: Measurements recorded on the perpendicular and on a 25-degree tilt showed no statistically significant difference between conventional and accelerated groups. All gap measurements except one were within the range of clinical acceptability. The measurements revealed that conventional and accelerated perpendicular gap means were 13.2 and 13.6 microm, respectively, and the average tilted gap means were 31.6 and 32.2 microm, respectively. CONCLUSIONS: A phosphate-bonded investment (Ceramigold) selected for an accelerated casting technique produced single castings within 30 minutes with marginal gaps comparable to those found that used conventional methods.

Crowns↗

PubMed2002

Sensitivity of a disc rupture strength test to air bubble pores in phosphate-bonded investment materials at elevated temperatures.

OBJECTIVES: To investigate the sensitivity of a modified disc rupture test to variables affecting the strength of four phosphate-bonded investment materials under conditions closely resembling the in-service environment. This study examined the influence of air bubble pores on the strength of phosphate bonded investment materials at a temperature of 900 degrees C. METHODS: A modified disc rupture configuration was used to test a circular investment diaphragm with clamped edges, in tension, initiated by bending. A sequentially-varying molten metal mass was used to apply the load using an electronic centrifugal casting machine. The staircase method was used to determine the increase or decrease of the applied load with the standardized increment of load being no greater than 1 or 2g. The mean load applied to 30 samples defined the transition of survival to failure of the investment disc and was taken as a measurement of investment strength. Two material handling techniques, one giving virtually no pores and one showing a wide pore size distribution were used. RESULTS: The diaphragm clearly either failed or survived the test with the pattern of fracture indicating brittle failure. A statistically significant difference in strength (P<0.050) of diaphragms with and without air bubble pores was demonstrated for three materials. Fewer pores resulted in increased strength of those materials and produced a much reduced scatter of strength in the fourth. SIGNIFICANCE: The modified disc rupture test is sufficiently sensitive to identify variations in strength of phosphate bonded investment materials caused by differing pore size distributions.

Air↗

PubMed2003

Effect of burnout temperature on strength of gypsum-bonded investments.

OBJECTIVE: To investigate the variation of the strength of gypsum-bonded dental investments with burnout temperature. METHODS: The disc-rupture test was employed at burnout temperatures ranging from 450 to 800 degrees C for four products (Beauty Cast, Cristobalite, Novocast (all WhipMix) and Deguvest California (Degussa)). In this test, an investment disc is created inside an investment mold such that it forms a diaphragm across the mold space, being an integral part of the mold. Copper was cast into molds of this type, and whether the disc had ruptured or not was determined by inspection when cold. The amount of copper cast in successive tests was varied in staircase fashion up and down depending on whether the disc survived or failed. The strength of the investment was represented by the 50% point of the transition from survival to rupture. RESULTS: The strength of gypsum-bonded investment is temperature sensitive, there being marked differences between the products tested. Overall, the strength ranking (temperature range average/MPa) was: Cristobalite (10.1)>Beauty Cast (7.8)>Novocast (5.1)>Deguvest California (3.4). The strength ranking at high temperatures differs from that known for the room temperature values. SIGNIFICANCE: The use by manufacturers of room-temperature strength data conveys no information about high temperature behavior. Investment properties should be optimized by reference to behavior under casting conditions.

Calcium Sulfate↗

PubMed2003

Effect of zirconia-modified magnesia investment on the casting of pure titanium.

Several investigations have examined magnesia-based investments for pure titanium casting. However, the thermal expansion value was insufficient at low casting temperatures and high interfacial reactivity occurred at high casting temperatures. The purpose of this investigation was to modify a magnesia-based investment by adding a heat-resistant mold material, zirconia, in different ratios to produce a more accurate titanium casting. The thermal expansion value was measured using a new precise automatic laser recording machine and pure titanium was cast using an argon casting machine. The marginal accuracy was measured using a stereomicroscope and the interfacial reactivity of the titanium was evaluated using X-ray diffraction analysis. The results indicate that adding different amounts of zirconia to a magnesia-based investment can increase its thermal expansion value and decrease the interfacial reactivity of the titanium. Maximal thermal expansion in the zirconia-modified investments significantly increased by 5-6 weight % (wt%) and peaked at 1.62% expansion. Selevest with 5 wt% zirconia had the smallest mean marginal discrepancy, 21.70 microm at 750 degrees C. Analysis of variance indicates significant differences in marginal discrepancy between zirconia-modified investments (p < 0.001). Adding zirconia can also decrease the interfacial reactivity of the titanium. The data indicated that proper amounts of zirconia (5-6 wt%) added to a magnesia-based investment can produce a more accurate and less interfacial reactive pure titanium casting.

Dental Casting Investment↗

PubMed1986

Particle and pore size distributions of investments.

The particle-size distributions of investment powders and the pore-size distributions of set-fired investments were investigated by electrozone size analysis, and by mercury intrusion scanning porosimetry, respectively, for a number of different investments, representing all three types available, namely: the gypsum-, phosphate- and silicate-bonded. The pore volume (V), the pore surface area (S), and their first derivatives with respect to radius, r, dV/dr and dS/dr, were obtained with pressures up to 414 MPa corresponding to spherical pores of 0.0018 micron radius if the Washburn equation is to apply. Results distinguished pores with a range of different sizes. Besides the porosity due to the matrix binder, porosity was also attributable to the refractory components. This latter type of porosity occurred with pore radii below about 0.03 micron, whereas matrix porosity occurred above this pore size. Matrix porosity for the phosphate materials was smallest at about 0.03 to 0.5 micron in radius, followed by the gypsum materials at about 0.3 to 0.6 micron, and by the silicate materials at about 1 to 10 micron. The particle-size distribution of the investment powders may affect both types of porosities, whereas the setting chemistries of the particular investment types may affect matrix porosity, by the generation of gaseous by-products. No major distinctions in pore size and distributions occurred between air-set and hygroscopic-set materials. This study emphasizes that at present, knowledge of the total pore volume only is inadequate for characterizing porosity distribution and hence investment permeability.

Calcium Sulfate↗

PubMed2004

Return on investment.

Return on investment is an excellent mechanism for evaluating large practice purchasing decisions. Whether you are purchasing a new practice, opening an office, building a new facility, recruiting an associate or adding technology, the issue that always should be evaluated is whether the investment will create a positive return for the practice and, if so, in what period. While most dental investments actually provide a positive return on investment within 12 months, larger investments, such as purchasing a practice or opening new offices, may require several years to gain a positive return. They still may be good decisions. At the very least, return-on-investment considerations allow dentists to evaluate options from a business-plan perspective, rather than simply making uninformed decisions.

Capital Expenditures↗

PubMed2000

Study of resin-bonded calcia investment: Part 1. Setting time and compressive strength.

This study was carried out to develop a new titanium casting investment consisting of calcia as the refractory material and a cold-curing resin system as the binder. The setting time of the investment was investigated under different N,N-dimethyl-p-toluidine (DMPT) contents in methyl methacrylate monomer (MMA) and benzoyl peroxide (BPO) contents in calcia without any sintering agent. The effects of the sintering agents, which were calcium fluoride (CaF2) and calcium chloride (CaCl2), on the compressive strength of the investments were investigated at room temperature before and after heating to two different temperatures. The shortest setting time (68 minutes) of the investment was obtained at 0.37 DMPT/BPO (1.5 vol% /1.0 mass%) ratio by mass. The highest strength (16.5 MPa) was obtained from the investment which contained 2 mass% CaF2 and was heated to 1,100 degrees C. It was found that the developed calcia investment containing 2 mass% CaF2 has a possibility for use in titanium castings.

Alloys↗