Transforming growth factor beta (TGF-β) is a polypeptide found in high concentrations in bone and is produced by and acts on primary adult human derived osteoblast-enriched cultures (PHO cells). Receptors for TGF-β are present on PHO cells and TGF-β is mitogenic for these cells. Results of these studies in conjunction with those of others suggest that TGF-β may have an important therapeutic role in orthopaedic surgery; however, with respect to its mitogenic actions, further studies were needed to establish whether TGF-β was acting directly to stimulate the growth of PHO cells. TGF-β has been found in other systems to act as an indirect mitogen, stimulating growth via secretion of another growth factor, platelet-derived growth factor (PDGF). In an effort to determine whether the TGF-β growth stimulation was mediated directly or indirectly, we have examined the growth stimulation of PHO cells by PDGF alone and in combination with TGF-β. These studies revealed that TGF-p in combination with either PDGF-AA or BB led to stimulation greater than that observed with either growth factor alone. TGF-P in combination with PDGF-BB led to a synergistic stimulatory response while that observed with the AA isoform was more nearly additive. Further studies demonstrated that TGF-β was capable of up-regulating the protein levels of the PDGF alpha (α) receptor within thirty minutes of TGF-β pretreatment. Thus, TGF-β appears to have both direct and indirect mechanisms of action as a mitogen in the PHO system. Finally, we showed that both the positive and negative alkaline phosphatase staining PHO cells were responsive to the mitogenic effects of both growth factor singly and in combination.
This study compares dry stopping performance of various foundation brake systems on Class VIII truck tractors. Four configurations of foundation brakes were fitted to two modern 6x4 conventional truck tractors without modification to the control, application or antilock brake systems. The foundation brake configurations included: standard S-cam drum brakes on all six positions, high output S-cam drum and then air disc brakes on the steer axles, and air disc brakes on all six brake positions. The stopping distances from 60 mph were analyzed for all test conditions. The truck tractors were tested in two weight configurations: LLVW (i.e., bobtail) and GVWR (50,000 lb total axle weight) using an unbraked control semitrailer. Analysis of variance tests indicate statistically different stopping distance means between all foundation brake configurations, whether the results for both weight configurations were combined or analyzed separately. Combining the results for both tractors, an all disc brake configuration could yield a 20% improvement in stopping distance at GVWR over the standard all S-cam brake configuration on dry pavement, and a 16% improvement at LLVW. With hybrid disc brakes, the improvements were 12% for GVWR and 19% for LLVW. For hybrid drum brakes, the improvements were 10% for both GVWR and LLVW. Margins of compliance for the minimum stopping distances (versus a 30% reduction in current standards) are shown for each brake configuration.
AbstractPrimary human osteoblast-enriched (PHO) cultures derived from adult trabecular bone were analyzed to determine the presence or absence of transforming growth factor beta (TGF-β) receptors. Saturation binding studies were performed with 125I-TGF-β in the absence or presence of 200-fold excess cold TGF-β. Cross-linking experiments utilizing 125-I-TGF-β were performed to identify specific cell surface binding proteins for TGF-β. The saturation binding studies demonstrated saturable binding for TGF-β on PHO cells. TGF-β was cross-linked to cell surface binding proteins of 50 to 110 KDa and a high molecular weight component. Thus, these receptors appear to be similar in affinity, number per cell, and molecular weight to those previously identified with other cell types. The potential biological effects of TGF-β on the growth of PHO cultures were evaluated by both 3H-thymidine incorporation and cell number determination. Growth of PHO cells in the presence of TGF-β resulted in an approximately two-fold stimulation in cell number as compared to control cells while the 3H-thymidine experiments demonstrated a two to four-fold increase in thymidine uptake in the presence of TGF-β. Radiographic emulsion studies revealed that the alkaline phosphatase positive and negative cell populations were responsive to the TGF-β mitogenic stimulation. The cumulative findings of saturable binding, specific cell surface binding proteins, and biological effects suggest that functional TGF-β cell surface receptors are present on primary osteoblast-enriched cultures derived from adult human trabecular bone.Key Words: human osteoblaststransforming growth factor betareceptorsmitogen
The effect of higher output foundation brakes were determined for a Class 8, Mack 6x4 MR-688-S straight truck which emulated a McNeilus refuse hauler. Four brake types studied included: original hybrid S-cam drums, big S-cam drums, hybrid disc, and all-disc. In order to simulate the completed refuse hauler, the mock-up truck was loaded in three configurations: fully laden at gross vehicle weight rating (GVWR), at lightly loaded vehicle weight (LLVW) simulating an unloaded refuse hauler, and empty (MT) for comparison to other chassis-cab test trucks. The results show that the chassis-cab mock-up truck with hybrid S-cam brakes produced performance data similar to that obtained from the McNeilus refuse hauler for most tests, which indicated that the mock-up was realistic in loading configuration and in braking capability. At GVWR, the test truck stopped in 298 ft, which correlated to the 302 ft obtained by the refuse hauler. By installing higher output brakes, the service brake stopping distances shortened dramatically. The all-disc brakes performed the best (228 ft), followed closely by the hybrid disc brakes (245 ft) and the big S-cam drum brakes (248 ft). For baseline brake-in-a-curve (BIC) tests, all four brake configurations met the minimum stability and control test requirement; therefore, increasing the brake output made little change in stability on the low-coefficient-of-friction surface. Additional loads of GVWR and MT produced similar results at the 75-percent of drive-through “target speed” for four-of-four tests. For limit-speed tests, the highest lateral acceleration performance quotient (LAPQ) values were achieved by the hybrid S-cam and big S-cam brake configurations. Each load and brake configuration applied to the chassis-cab mock-up truck met the 5-minute parking brake holding requirement of the Federal Motor Vehicle Safety Standard (FMVSS) No. 121 on the 20-percent grade, which was also found previously for the refuse hauler. This pass/fail test could not distinguish any differences in brake type installed on this vehicle. However, the drawbar parking brake force test showed large differences in parking brake holding ability. The 2005 test results showed that the refuse hauler failed the drawbar test for the rearward pull direction on the rear axle by over one percent. However, the mock-up vehicle met the minimum required drawbar force. The higher output all-disc and big S-cam brakes produced drawbar margins of compliance ranging from 35 to 105 percent, with the big S-cam brakes producing the largest margins in the rearward pull direction. Split-mu tests showed little difference in stopping distances or decelerations between the four brake types tested. The decelerations did indicate a side-to-side bias in total vehicle response to the stops on this surface, which were substantiated by driver comments and handwheel angle data. When loaded to GVWR and LLVW, the big S-cam brakes required the biggest driver handwheel inputs of the four brake types indicating that wider S-cam brakes are more sensitive to side-to-side brake imbalance issues.
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