Is high-altitude mountaineering Russian roulette?

2013 ◽  
Vol 9 (1) ◽  
pp. 1-14 ◽  
Author(s):  
Edward K. Cheng
Keyword(s):  
High Altitude ◽  
Failure Rate ◽  
Rate Model ◽  
Reliability Engineering ◽  
Significant Difference ◽  
Inference Techniques ◽  
Decreasing Failure Rate

AbstractWhether the nature of the risks associated with climbing high-altitude (8000 m) peaks is in some sense “controllable” is a longstanding debate in the mountaineering community. Well-known mountaineers David Roberts and Ed Viesturs explore this issue in their recent memoirs. Roberts views the primary risks as “objective” or uncontrollable, whereas Viesturs maintains that experience and attention to safety can make a significant difference. This study sheds light on the Roberts-Viesturs debate using a comprehensive dataset of climbing on Nepalese Himalayan peaks. To test whether the data is consistent with a constant failure rate model (Roberts) or a decreasing failure rate model (Viesturs), it draws on Total Time on Test (TTT) plots from the reliability engineering literature and applies graphical inference techniques to them.

Outcomes of Inside-out Meniscal Repair in the Setting of Multiligament Reconstruction in the Knee

2017 ◽  
Vol 45 (9) ◽  
pp. 2098-2104 ◽  
Author(s):  
Jorge Chahla ◽  
Chase S. Dean ◽  
Lauren M. Matheny ◽  
Justin J. Mitchell ◽  
Mark E. Cinque ◽  
...  
Keyword(s):  
Failure Rate ◽  
Meniscal Repair ◽  
Postoperative Outcome ◽  
Control Group ◽  
Failure Rates ◽  
Significant Difference ◽  
Outcome Scores ◽  
Inside Out ◽  
Repair Group

Background: Limited evidence exists for meniscal repair outcomes in a multiligament reconstruction setting. Purpose/Hypothesis: The purpose of this study was to assess outcomes and failure rates of meniscal repair in patients who underwent multiligament reconstruction compared with patients who underwent multiligament reconstruction but lacked meniscal tears. The authors hypothesized that the outcomes of meniscal repair associated with concomitant multiligament reconstruction would significantly improve from preoperatively to postoperatively at a minimum of 2 years after the index surgery. Secondarily, they hypothesized that this cohort would demonstrate similar outcomes and failure rates compared with the cohort that did not have meniscal lesions at the time of multiligament reconstruction. Study Design: Cohort study; Level of evidence, 3. Methods: Inclusion criteria for the study included radiographically confirmed skeletally mature patients of at least 16 years of age who underwent multiligamentous reconstruction of the knee without previous ipsilateral osteotomy, intra-articular infections, or intra-articular fractures. Patients were included in the experimental group if they underwent inside-out meniscal suture repair with concurrent multiligament reconstruction. Those included in the control group (multiligament reconstruction without a meniscal tear) underwent multiligament reconstruction but did not undergo any type of meniscal surgery. Lysholm, Western Ontario and McMaster Universities Osteoarthritis Index, Short Form–12 physical component summary and mental component summary, Tegner activity scale, and patient satisfaction scores were recorded preoperatively and postoperatively. The failure of meniscal repair was defined as a retear of the meniscus that was confirmed arthroscopically. Results: There were 43 patients (16 female, 27 male) in the meniscal repair group and 62 patients (25 female, 37 male) in the control group. Follow-up was obtained in 93% of patients with a mean of 3.0 years (range, 2.0-4.7 years). There was a significant improvement between all preoperative and postoperative outcome scores ( P < .05) for both groups. The meniscal repair group had significantly lower preoperative Lysholm and Tegner scores ( P = .009 and P = .02, respectively). There were no significant differences between any other outcome scores preoperatively. The failure rate of the meniscal repair group was 2.7%, consisting of 1 symptomatic meniscal retear. There was no significant difference in any postoperative outcome score at a minimum 2-year follow-up between the 2 groups. Conclusion: Good to excellent patient-reported outcomes were reported for both groups with no significant differences in outcomes between the cohorts. Additionally, the failure rate for inside-out meniscal repair with concomitant multiligament reconstruction was low, regardless of meniscus laterality and tear characteristics. The use of multiple vertical mattress sutures and the biological augmentation resulting from intra-articular cruciate ligament reconstruction tunnel reaming may be partially responsible for the stability of the meniscal repair construct and thereby contribute to the overall improved outcomes and the low failure rate of meniscal repair, despite lower preoperative Lysholm and Tegner scores in the meniscal repair group.

scholarly journals Clinical Evaluation of Bracket Bonding Using Two Different Polymerization Sources

2008 ◽  
Vol 78 (5) ◽  
pp. 922-925 ◽  
Author(s):  
Nikolaos S. Koupis ◽  
Theodore Eliades ◽  
Athanasios E. Athanasiou
Keyword(s):  
Failure Rate ◽  
Orthodontic Treatment ◽  
Light Emitting Diode ◽  
Rank Test ◽  
Dental Arch ◽  
Halogen Lamp ◽  
Failure Rates ◽  
Bond Failure ◽  
Significant Difference ◽  
The Right

Abstract Objective: To comparatively assess clinical failure rate of brackets cured with two different photopolymerization sources after nine months of orthodontic treatment. Materials and Methods: The sample of this study comprised 30 patients who received comprehensive orthodontic treatment by means of fixed appliances. Using the same adhesive, 600 stainless steel brackets were directly bonded and light cured for 10 seconds with the light-emitting diode (LED) lamp or for 20 seconds with the conventional halogen lamp. A split-mouth design randomly alternated from patient to patient was applied. Failure rates were recorded for nine months and analyzed with Pearson χ2 test, and log-rank test at α = .05 level of significance. Results: The overall failure rate recorded with the halogen unit (3.33%) was not significantly different from the failure rate for the LED lamp (5.00%). Significantly more failures were found in boys compared with girls, in the mandibular dental arch compared with the maxillary arch, and in posterior segments compared with anterior segments. However, no significant difference was found between the right and left segments. Conclusion: Both light-curing units showed sufficiently low bond failure rates. LED curing units are an advantageous alternative to conventional halogen sources in orthodontics because they enable a reduced chair-time bonding procedure without significantly affecting bond failure rate.

Stochastic inequalities for an overflow model

1987 ◽  
Vol 24 (3) ◽  
pp. 696-708 ◽  
Author(s):  
Arie Hordijk ◽  
Ad Ridder
Keyword(s):  
Failure Rate ◽  
Lower Bounds ◽  
Approximation Method ◽  
Queueing Networks ◽  
Upper And Lower Bounds ◽  
Phase Type ◽  
Phase Type Distributions ◽  
Decreasing Failure Rate ◽  
General Method

A general method to obtain insensitive upper and lower bounds for the stationary distribution of queueing networks is sketched. It is applied to an overflow model. The bounds are shown to be valid for service distributions with decreasing failure rate. A characterization of phase-type distributions with decreasing failure rate is given. An approximation method is proposed. The methods are illustrated with numerical results.

scholarly journals Clinical evaluation of the failure rate of metallic brackets bonded with orthodontic composites

2012 ◽  
Vol 23 (4) ◽  
pp. 399-402 ◽  
Author(s):  
Fábio Lourenço Romano ◽  
Rodrigo Alexandre Valério ◽  
Jaciara Miranda Gomes-Silva ◽  
José Tarcísio Lima Ferreira ◽  
Gisele Faria ◽  
...  
Keyword(s):  
Failure Rate ◽  
Orthodontic Treatment ◽  
Color Change ◽  
Rank Test ◽  
Initial Alignment ◽  
Bond Failure ◽  
Log Rank Test ◽  
Significant Difference ◽  
Mandibular Teeth

The purpose of the present study was to evaluate in vivo the failure rate of metallic brackets bonded with two orthodontic composites. Nineteen patients with ages ranging from 10.5 to 38.7 years needing corrective orthodontic treatment were selected for study. The enamel surfaces from second premolars to second premolars were treated with Transbond Plus-Self Etching Primer (3M Unitek). Next, 380 orthodontic brackets were bonded on maxillary and mandibular teeth, as follows: 190 with Transbond XT composite (3M Unitek) (control) and 190 with Transbond Plus Color Change (3M Unitek) (experimental) in contralateral quadrants. The bonded brackets were light cured for 40 s, and initial alignment archwires were inserted. Bond failure rates were recorded over a six-month period. At the end of the evaluation, six bond failures occurred, three for each composite. Kaplan-Meyer method and log-rank test (Mantel-Cox) was used for statistical analysis, and no statistically significant difference was found between the materials (p=0.999). Both Transbond XT and Transbond Plus Color Change composites had low debonding rates over the study period.

scholarly journals Evaluation of Bond Failure Rate of Orthodontic Brackets Bonded with Green Gloo-Two Way Color Changes Adhesive: A Clinical Study

1970 ◽  
Vol 29 (2) ◽  
Author(s):  
Zuber Ahamed Naqvi ◽  
Saleem Shaikh ◽  
Zameer Pasha
Keyword(s):  
Failure Rate ◽  
Sampling Technique ◽  
Orthodontic Brackets ◽  
Rank Test ◽  
Dental Arch ◽  
Failure Rates ◽  
Bond Failure ◽  
Color Changes ◽  
Kaplan Meier ◽  
Significant Difference

BACKGROUND: Bonding is an important step in fixed orthodontic mechanotherapy. Many new materials introduced an adhesive for bonding. This study was designed to evaluate the clinical bond failure rate of orthodontic brackets bonded with green glue: two way color changes adhesive and transbond XT adhesive paste.METHODS: Eighteen male patients with a mean age of 16 years were included in the study. Convenience sampling technique was used to select the sample for this study. The split-mouth design was used to bond 360 brackets by one operator and both adhesives were used in each patient. Bond failure rates were estimated with respect to bonding procedure, dental arch, tooth type (incisor, canine, and premolar). The results were evaluated using the chisquare test. Kaplan – Meier analysis and the log rank test were used to estimate the survival rate of the brackets. Bracket failure rates for each system were analyzed, and failure causes as reported by the patients and the quadrant of each tooth in which bracketsfailed were recorded.RESULTS: The bond failure rate was 5.00% and 4.44% for green gloo and transbond XT group. No significant difference was found in the bond failure rate between transbond XT and Green gloo group. No significant difference was found in the bond failure rate between the two groups, in relation to right and left side and the type of teeth.CONCLUSION: Green gloo adhesive can be effectively used to bond orthodontic brackets.

scholarly journals LED vs Halogen Light-Curing of Adhesive-Precoated Brackets

2008 ◽  
Vol 78 (5) ◽  
pp. 935-940 ◽  
Author(s):  
Davide Mirabella ◽  
Raffaele Spena ◽  
Giovanni Scognamiglio ◽  
Lombardo Luca ◽  
Antonio Gracco ◽  
...  
Keyword(s):  
Failure Rate ◽  
Rank Test ◽  
Fisher Exact Test ◽  
Halogen Lamp ◽  
Chi Square ◽  
Halogen Light ◽  
Significant Difference ◽  
Chi Square Test ◽  
Light Curing ◽  
Bracket Failure

Abstract Objective: To test the hypothesis that bonding with a blue light-emitting diode (LED) curing unit produces no more failures in adhesive-precoated (APC) orthodontic brackets than bonding carried out by a conventional halogen lamp. Materials and Methods: Sixty-five patients were selected for this randomized clinical trial, in which a total of 1152 stainless steel APC brackets were employed. In order to carry out a valid comparison of the bracket failure rate following use of each type of curing unit, each patient's mouth was divided into four quadrants. In 34 of the randomly selected patients, designated group A, the APC brackets of the right maxillary and left mandibular quadrants were bonded using a halogen light, while the remaining quadrants were treated with an LED curing unit. In the other 31 patients, designated group B, halogen light was used to cure the left maxillary and right mandibular quadrants, whereas the APC brackets in the remaining quadrants were bonded using an LED dental curing light. The bonding date, the type of light used for curing, and the date of any bracket failures over a mean period of 8.9 months were recorded for each bracket and, subsequently, the chi-square test, the Yates-corrected chi-square test, the Fisher exact test, Kaplan-Meier survival estimates, and the log-rank test were employed in statistical analyses of the results. Results: No statistically significant difference in bond failure rate was found between APC brackets bonded with the halogen light-curing unit and those cured with LED light. However, significantly fewer bonding failures were noted in the maxillary arch (1.67%) than in the mandibular arch (4.35%) after each light-curing technique. Conclusions: The hypothesis cannot be rejected since use of an LED curing unit produces similar APC bracket failure rates to use of conventional halogen light, with the advantage of a far shorter curing time (10 seconds).

scholarly journals Tropical tropospheric ozone derived using Clear-Cloudy Pairs (CCP) of TOMS measurements

2003 ◽  
Vol 3 (1) ◽  
pp. 225-252 ◽  
Author(s):  
M. J. Newchurch ◽  
D. Sun ◽  
J. H. Kim ◽  
X. Liu
Keyword(s):  
High Altitude ◽  
Tropospheric Ozone ◽  
Total Ozone ◽  
Stratospheric Ozone ◽  
Lower Troposphere ◽  
Total Ozone Mapping Spectrometer ◽  
Significant Difference ◽  
Retrieval Efficiency ◽  
Retrieval Errors ◽  
Low Altitude

Abstract. Using TOMS total-ozone measurements over high-altitude cloud locations and nearby paired clear locations, we describe the Clear-Cloudy Pairs (CCP) method for deriving tropical tropospheric ozone. The high-altitude clouds are identified by measured 380 nm reflectivities greater than 80% and Temperature Humidity InfraRed (THIR) measured cloud-top pressures less than 200 hPa. To account for locations without high-altitude clouds, we apply a zonal sine fitting to the stratospheric ozone derived from available cloudy points, resulting in a wave-one amplitude of about 4 DU. THIR data is unavailable after November 1984, so we extend the CCP method by using a reflectivity threshold of 90% to identify high-altitude clouds and remove the influence of high-reflectivity-but-low-altitude clouds with a lowpass frequency filter. We correct ozone retrieval errors associated with clouds, and ozone retrieval errors due to sun glint and aerosols. Comparing CCP results with Southern Hemisphere ADditional OZonesondes (SHADOZ) tropospheric ozone indicates that CCP tropospheric ozone and ozonesonde measurements are highly consistent. The most significant difference between CCP and ozonesonde tropospheric ozone can be explained by the low Total Ozone Mapping Spectrometer (TOMS) retrieval efficiency of ozone in the lower troposphere.

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