Failure Predictions of Out-of-Autoclave Sandwich Joints with Delaminations Under Flexure Loads

An analysis and a test program was conducted to investigate the damage tolerance of composite sandwich joints. The joints contained a single circular delamination between the face-sheet and the doubler. The coupons were fabricated through out-of-autoclave (OOA) processes, a technology NASA is investigating for joining large composite sections. The four-point bend flexure test was used to induce compression loading into the side of the joint where the delamination was placed. The compression side was chosen since it tends to be one of the most critical loads in launch vehicles. Autoclave cure was used to manufacture the composite sandwich sections, while the doubler was co-bonded onto the sandwich face-sheet using an OOA process after sandwich panels were cured. A building block approach was adopted to characterize the mechanical properties of the joint material, including the fracture toughness between the doubler and face-sheet. Twelve four-point-bend samples were tested, six in the sandwich core ribbon orientation and six in sandwich core cross-ribbon direction. Analysis predicted failure initiation and propagation at the pre-delaminated location, consistent with experimental observations. Fracture analyses methods predicted failure loads in close agreement with tests. This investigation demonstrated a strength reduction of 10 percent due to a flaw of significant size compared to the width of the sample. Therefore, concerns of bonding an OOA material to an in-autoclave material was mitigated for the geometries, materials, and load configurations considered

Failure Predictions of Out-of-Autoclave Sandwich Joints with Delaminations under Flexure Loads

An analysis and a test program was conducted to investigate the damage tolerance of composite sandwich joints. The joints contained a single circular delamination between the face-sheet and the doubler. The coupons were fabricated through out-of-autoclave (OOA) processes, a technology NASA is investigating for joining large composite sections. The four-point bend flexure test was used to induce compression loading into the side of the joint where the delamination was placed. The compression side was chosen since it tends to be one of the most critical loads in launch vehicles. Autoclave cure was used to manufacture the composite sandwich sections, while the doubler was co-bonded onto the sandwich face-sheet using an OOA process after sandwich panels were cured. A building block approach was adopted to characterize the mechanical properties of the joint material, including the fracture toughness between the doubler and facesheet. Twelve four-point-bend samples were tested, six in the sandwich core ribbon orientation and six in sandwich core cross-ribbon direction. Analysis predicted failure initiation and propagation at the pre-delaminated location, consistent with experimental observations. A building block approach using fracture analyses methods predicted failure loads in close agreement with tests. This investigation demonstrated a small strength reduction due to a flaw of significant size compared to the width of the sample. Therefore, concerns of bonding an OOA material to an in-autoclave material was mitigated for the geometries, materials, and load configurations considered

Cardiac Risk Factors Predicting 30/90 Day Readmission Rates in Lumbar Decompression Surgeries

Preoperative cardiopulmonary disease is known to be a risk factor for perioperative complications in deformity surgery and lumbar fusion procedures, however there is a lack of literature evaluating cardiac risk factors and their influence on readmission rates following lumbar decompression surgery. We want to determine whether preoperative cardiac risk factors influenced the 30 and 90-day readmission rates in patients undergoing lumbar decompression surgery. Patient charts from Rothman Institute between were reviewed for history of preoperative cardiac risk factors such as coronary artery disease, congestive heart failure, myocardial infarction, stroke, cardiac catheterization, stent placement, coronary artery bypass graft, aspirin and/or clopidogrel use. Binary logistic regression was used to determine whether or not these risk factors predicted 30-day and 90-day readmissions for patients undergoing lumbar decompression surgery. Overall, the total number of 30-day readmissions was 33 (3.55%) and the number of 90-day readmissions was 46 (4.95%). No cardiac risk factor was found to be a significant predictor of 30-day readmission rates. Use of aspirin, 81 mg, was found to negatively predict readmission rate at 90 days (OR = 0.192 [0.042, 0.881], p = 0.034). Cardiac risk factors are known to increase surgical morbidity. The results of this study show that patients taking aspirin 81 mg preoperatively exhibited significantly lower odds of undergoing an unplanned readmission at 90 days after a lumbar decompression procedure. No significant risk factors for 30-day readmissions were found. Taking aspirin may confer a protective benefit perioperatively in a high-risk population

To evaluate the effects of lubricating eye drops on the repeatability of keratometry (K) measurements in patients presenting for cataract surgery

Purpose – To evaluate the effects of lubricating eye drops on the repeatability of keratometry (K) measurements in patients presenting for cataract surgery. Design – Prospective, Comparative, Hospital-based study. Method – K readings were taken using the automatic keratometer of an autorefractometer. At Study Visit 1, keratometry was performed twice consecutively before instilling any eye drops. After instilling artificial tears, K readings were taken at 30 seconds and 2 minutes. Tear Break-Up Time (TBUT) was measured, and patients were divided into two groups [normal and dry eye]. The next morning, a second set of readings was taken. At Study Visit 2, one week post-surgery, a third set of K1 and K2 readings was recorded. Result – This study investigates variations in keratometry readings (K1 and K2) across different time points and between normal and dry eye patients. At Study Visit 1, keratometry was measured before and after the instillation of artificial tears, with readings taken at multiple intervals. Post-hoc analysis reveals significant differences in the mean K1 values between various time points within the dry eye group, with p-values consistently below 0.0001. Additionally, significant differences were found between normal and dry eyes at 0.5 minutes and 2 minutes post-instillation

Opioid Tolerance Influences Outcomes after Lumbar Fusion in Patients with Degenerative Pathology

Introduction: Extended opioid use prior to surgery has been implicated in poorer postoperative outcomes. However, it remains unclear if there is a significant difference in postoperative outcomes among preoperative opioid-naïve and opioid-tolerant patients who undergo lumbar spinal fusion. The purpose of this study was to determine the effect of preoperative opioid use on patient-reported outcome measures in patients undergoing lumbar spinal fusion. Methods: This retrospective cohort analysis identified 260 patients who underwent lumbar spinal fusion at a high-volume, single institution. There were two cohorts: patients who were opioid-naïve (defined as total opioid consumption of ≤ 7 days in the two months prior to surgery) and opioid-tolerant users (\u3e 7 days). Outcome measures were analyzed via the number of and duration of opioid tablets consumed, and patient-reported outcome measures (ODI, SF-12 PCS and MCS, and VAS Back and Leg pain scores). Results: Overall, opioid-naïve patients were prescribed significantly fewer tablets on average compared to opioid-tolerant users. The number of tablets prescribed prior to surgery was a predictor for prolonged opioid use—defined as greater than one script after surgery. Opioid-tolerant users had decreased improvement in outcomes postoperatively compared to opioid-naïve users. Discussion: This study suggests that preoperative opioid-tolerant usage was associated with worse outcome scores postoperatively. Opioid-tolerant users were found to have significantly more pain medication tablets preoperatively and for a longer duration postoperatively. Therefore, opioid-tolerant usage can adversely affect patient outcomes and is a modifiable risk factor prior to undergoing lumbar spinal fusion

Experimental Evaluation of a Small-capacity, Direct-fired Ammonia-water Absorption Chiller

Vapor absorption heating and cooling systems, utilizing heat input from different sources such as waste heat or natural gas, are attracting increasing interest in commercial and residential applications. Residential heat pump applications require compact heat exchanger geometries to ensure a small system footprint. Compact microscale heat and mass exchangers are developed and implemented here. These novel heat and mass exchanger geometries for different components of the system require evaluation at design and off-design conditions to characterize the individual component and overall system performance. This study presents results from experimental investigations of a small-capacity ammonia-water absorption chiller. The chiller comprises discrete heat and mass exchangers with novel design features, and is installed on a breadboard test facility. The absorber and condenser are directly coupled to ambient air and designed to operate at extreme ambient temperatures as high as 51.67°C. The microchannel evaporator is hydronically coupled. The desorber is direct-fired and coupled to a hot air-stream simulating a waste heat source. The system is designed to deliver 2.64 kW of cooling at a coefficient of performance (COP) of 0.55 based on the cooling duty and the desorber heat input rate. A steady-state model to specify various state-points in the system is developed. The experimental setup and details of heat exchanger geometries, measurement and instrumentation, and data analysis are presented. The overall system and component performance is evaluated to determine system limitations. The evaluation is conducted at lower ambient conditions of 35-40°C and the system model is modified to account for the corresponding changes. Results from baseline system operation at design mass flow rates of concentrated solution and heat input rates are presented. The performance of individual components is analyzed and compared to design predictions. Various operating conditions in the system such as the flow rate of concentrated and refrigerant solution, the heat source temperature and flow rates, and ambient temperature are varied to study the effect on the overall system and component performance.   The results from this investigation demonstrate the potential of small-capacity absorption chillers using microchannel and direct air-coupled heat exchangers, and will guide the development of a packaged waste-heat-driven chiller operating at extreme ambient conditions

Functional Outcomes after Lumbar Fusion in Opioid-Tolerant Patients

Introduction: Prolonged opioid use after lumbar fusion surgery is implicated with increased hospital readmissions, higher postoperative pain scores, and longer return to work time. There are several non-modifiable risk factors for postoperative opioid use including socioeconomic status and gender. The purpose of this study was to determine the effects of opioid-tolerance on PROMs and to determine risk factors for prolonged opioid use after lumbar spine surgery. Method: Using retrospective cohort analysis, patients who underwent lumbar spinal fusion at TJUH were identified and determined to be either opioid-naïve or opioid-tolerant using the Pennsylvania PDMP. Outcomes included number of opioid tablets consumed, duration of time using opioids, and patient-reported outcome measures (ODI, PCS-12, MCS-12, VAS Back, VAS Leg). Univariate and multivariate analysis were used to compare outcomes between the two groups. Logistic regression was used to determine independent predictors for prolonged opioid use which was defined as greater than one postoperative opioid prescription script filled. Results: A total of 260 patients were included in the final cohort, of which, 138 were opioid-tolerant and 122 were opioid naïve. Opioid-tolerant patients showed decreased improvement in PROMs compared to the opioid-naïve patients (p=0.043). The number of preoperative pills prescribed was a significant predictor for prolonged opioid use after lumbar fusion. Conclusion: The number of pills prescribed preoperatively was found to be a predictor for prolonged opioid use after lumbar fusion surgery. Overall, our results demonstrated that naïve patients have improved health-related quality of life outcome scores compared to opioid-tolerant patients after lumbar fusion