Statistical quality control through overall vibration analysis

The present study introduces the concept of statistical quality control in automotive wheel bearings manufacturing processes. Defects on products under analysis can have a direct influence on passengers’ safety and comfort. At present, the use of vibration analysis on machine tools for quality control purposes is not very extensive in manufacturing facilities.Noise and vibration are common quality problems in bearings. These failure modes likely occur under certain operating conditions and do not require high vibration amplitudes but relate to certain vibration frequencies. The vibration frequencies are affected by the type of surface problems (chattering) of ball races that are generated through grinding processes.The purpose of this paper is to identify grinding process variables that affect the quality of bearings by using statistical principles in the field of machine tools. In addition, an evaluation of the quality results of the finished parts under different combinations of process variables is assessed. This paper intends to establish the foundations to predict the quality of the products through the analysis of self-induced vibrations during the contact between the grinding wheel and the parts. To achieve this goal, the overall self-induced vibration readings under different combinations of process variables are analysed using statistical tools. The analysis of data and design of experiments follows a classical approach, considering all potential interactions between variables. The analysis of data is conducted through analysis of variance (ANOVA) for data sets that meet normality and homoscedasticity criteria. This paper utilizes different statistical tools to support the conclusions such as chi squared, Shapiro–Wilks, symmetry, Kurtosis, Cochran, Hartlett, and Hartley and Krushal–Wallis.The analysis presented is the starting point to extend the use of predictive techniques (vibration analysis) for quality control. This paper demonstrates the existence of predictive variables (high-frequency vibration displacements) that are sensible to the processes setup and the quality of the products obtained. Based on the result of this overall vibration analysis, a second paper will analyse self-induced vibration spectrums in order to define limit vibration bands, controllable every cycle or connected to permanent vibration-monitoring systems able to adjust sensible process variables identified by ANOVA, once the vibration readings exceed established quality limits.     

Impact of electric cardiac stimulation on ventricular function and the natural history of patients with myocardiopathy

There has recently been an increasing interest in beneficial effects of cardiac pacing in patients with myocardial diseases, especially in Obstructive Hypertrophic and Dilated Cardiomyopathy. The experience with dual-chamber pacing for obstructive hypertrophic cardiomyopathy is now important. DDD pacing for sinus rhythm patients and VVI pacing in patients with atrial fibrillation have shown considerable symptomatic improvement, with a significant decrease of angina, dyspnea, presyncope and frank syncope. It has been suggested that DDD pacing may prevent sudden death and improve survival rates in these patients, but this has not yet been established. The experience with DDD pacing in dilated cardiomyopathy is more limited, but in specially chosen patients, DDD pacing with short AV delay has shown symptomatic improvement and a decrease in the need for further hospitalization due to worsening of heart failure. There is no current evidence of higher survival rates with this treatment, but DDD pacing may be used in patients with end-stage dilated and isquemic cardiomyopathy who are waiting for a heart transplantation.     

Statistical quality control through process self-induced vibration spectrum analysis

The first part of this study (Carnero et al., Mechanical Systems and Signal Processing, 24:1138–1160, 2010) analysed the influence of the process variables and work cycles on the quality of the bearings manufactured in an automotive bearing plant. The study was focused on the analysis of the overall vibration reading produced by the contact between the tool and the part. An analysis of variance was conducted on the overall vibration readings, which reflected that high-frequency vibration displacements are sensitive to process setup variables as well as the quality of products manufactured. Nevertheless, it was also observed that overall vibration values are not sufficient to analyse the relationship between the mechanical behaviour (vibration) and final quality obtained from high-precision machining processes. In this article, therefore, a new study is conducted based on spectral vibration measurements. A new experiment has been designed taking as input variables the diameter and the rotating speed of the tool. The selection criterion is based on the strong influence of these two variables on high-frequency vibration displacement and quality of parts (chattering, measured in terms of Lob A and Lob B). Two identical grinding machine tools were used during the experimental phase. Output variables are high-frequency displacements and high- and low-frequency chattering. The statistical analysis used in the new experiments determines spectral bands of the process in which vibrations induced by tool–part contact relates to development of lobes in the part to be identified. The study allows identification of vibration bands that are suitable for control in order to guarantee quality of the parts produced. To achieve that goal, the concept of spectral identity of the processes has been introduced to incorporate vibration induced by the process itself in the spectrums and to differentiate that process vibration from other mechanical vibration sources.     

Maintenance treatment with interferon alpha-2b in multiple myeloma: a prospective randomized study from PETHEMA (Program for the Study and Treatment of Hematological Malignancies, Spanish Society of Hematology)

The objectives of the present study were to investigate whether interferon alpha (IFN) maintenance could prolong response duration and survival in patients with multiple myeloma (MM) in objective response and to analyze the characteristics of relapse and subsequent survival. From January 1991 to November 1994, 92 patients from the Spanish Cooperative Group PETHEMA with MM in objective response after 12 courses of VCMP/VBAP chemotherapy were randomized to receive IFN maintenance vs no treatment until relapse. Prognostic factors at diagnosis were similar in both groups. IFN was administered at a starting dose of 3 mU/m2 three times per week. The IFN toxicity was moderate with granulocytopenia and fatigue being the most common adverse effects. Median duration of response from randomization until relapse was 13 months in the IFN group vs 7.7 months in the no treatment arm (P = 0.042). Median survival from randomization was 38.8 months for patients given IFN vs 32.7 months for those allocated to the no treatment arm (P = 0.12). Features at relapse were similar in patients who received IFN maintenance and in those assigned to no treatment. Finally, survival from relapse was identical in both groups. In summary, our results show a significant prolongation of response in patients maintained with IFN with no significant influence on survival. In addition, in our series features at relapse and subsequent outcome were similar in both groups.     

Vibration analysis diagnostics by continuous-time models: A case study

In this paper a forecasting system in condition monitoring is developed based on vibration signals in order to improve the diagnosis of a certain critical equipment at an industrial plant. The system is based on statistical models capable of forecasting the state of the equipment combined with a cost model consisting of defining the time of preventive replacement when the minimum of the expected cost per unit of time is reached in the future. The most relevant features of the system are that (i) it is developed for bivariate signals; (ii) the statistical models are set up in a continuous-time framework, due to the specific nature of the data; and (iii) it has been developed from scratch for a real case study and may be generalised to other pieces of equipment. The system is thoroughly tested on the equipment available, showing its correctness with the data in a statistical sense and its capability of producing sensible results for the condition monitoring programme.     

Anatomical study of the cutaneous perforator arteries and vascularisation of the biceps femoris muscle

We present an anatomical study that describes the distribution of the cutaneous perforators (CP) of both heads of the biceps femoris muscle.

Material and methods

In this study, we dissected 18 legs from nine cadavers. The study was centered on the biceps femoris muscle and musculocutaneous perforator arteries from both muscular heads. Only perforator arteries with comitant vein diameters of over 0.5 mm were selected. The vascular origin and length were also studied. In all cases, measurements were taken from the bicondyle line.

Results

The measurements taken from the muscle bellies of the biceps gave the following results; for the long head 33.91 cm as medium length (SD=2.70) and for the short head 23.85 cm as medium length (SD=2.96).The total number of perforator arteries obtained from the two muscle bellies was 139, with the greatest percentage located in the lower half of the thigh. The majority follow an intramuscular route (80.48%) and less frequently they are septals (19.52%).The lengths of perforator arteries from its origin in the axial vessel of the muscle to the subcutaneous fat were, for the short head 5.01±1.33 (3.0–10.0), whereas the same measurement, in the long head was 4.54±1.36 (2.5–9.0).The principal vascular origin of the perforator arteries was the popliteal artery in both muscle bellies, whilst the second arterial vessel in importance was the first and second profunda perforator artery.

Conclusion

From the results obtained in our work, we can deduce that it is always possible to locate perforator arteries in both muscle bellies; most frequently they have intramuscular distribution and are located in the proximity of the vascular septum. Their most common origins are the popliteal artery and first and second profunda perforator artery. Finally, it is possible to design pedicle and free flaps, with less morbidity and more versatility than musculocutaneous flaps.     

Optimization of Maintenance in Production and Storage Systems for Domestic Water

Water Resources Management - Health care organizations are important consumers of domestic water, not only for human consumption, but also for the proper working of care services such as dialysis,...