Optical Design of Textured Thin-Film CIGS Solar Cells with Nearly-Invisible Nanowire Assisted Front Contacts.

The conductivity of transparent front contacts can be improved by patterned metallic nanowires, albeit at the cost of optical loss. The associated optical penalty can be strongly reduced by texturization of the cell stack. Remarkably, the nanowires themselves are not textured and not covered in our design. This was shown by optical modeling where the width of the nanowire, the texture height and the texture period were varied in order to obtain a good insight into the general trends. The optical performance can be improved dramatically as the reflection, which is the largest optical loss, can be reduced by 95% of the original value. The spectra reveal absorption in the Cu(In,Ga)Se2 (CIGS) layer of 95% and reflection below 2% over a large part of the spectrum. In essence, a virtually black CIGS cell stack can be achieved for textured cells with a metal nanogrid. Moreover, it turned out that the ratio between the width of the nanowire and the height of the texture is a critical parameter for optical losses.

Multi-Material Front Contact for 19% Thin Film Solar Cells.

The trade-off between transmittance and conductivity of the front contact material poses a bottleneck for thin film solar panels. Normally, the front contact material is a metal oxide and the optimal cell configuration and panel efficiency were determined for various band gap materials, representing Cu(In,Ga)Se2 (CIGS), CdTe and high band gap perovskites. Supplementing the metal oxide with a metallic copper grid improves the performance of the front contact and aims to increase the efficiency. Various front contact designs with and without a metallic finger grid were calculated with a variation of the transparent conductive oxide (TCO) sheet resistance, scribing area, cell length, and finger dimensions. In addition, the contact resistance and illumination power were also assessed and the optimal thin film solar panel design was determined. Adding a metallic finger grid on a TCO gives a higher solar cell efficiency and this also enables longer cell lengths. However, contact resistance between the metal and the TCO material can reduce the efficiency benefit somewhat.

How close does an uncemented hip stem match the final rasp position?

During total hip arthroplasty the final clinical position of the cementless CLS stem (Centerpulse) is not always identical to the position of the final rasp with which a successful trial reduction was performed. Therefore, the rasp-stem correspondence of CLS system (Centerpulse) was investigated in a laboratory study and compared to the CBC-T system (Mathys). Both systems showed an average rasp-stem mismatch below 2 mm in three orthogonal directions. It was found that this mismatch related to geometric differences at the corners between rasp and stem. The measured mismatch is not expected to have adverse clinical consequences.

The influence of open and closed high tibial osteotomy on dynamic patellar tracking: a biomechanical study.

High tibial osteotomy (HTO) can cause alterations in patellar height, depending on the surgical technique, the amount of correction and the postoperative management. Alterations in patella location after HTO may lead to postoperative complications. However, information on changes in dynamic patellar kinematics following HTO is very limited. We conducted a biomechanical study, to analyze the effect of open (OWO) and closed wedge osteotomy (CWO) on patellar tracking. Using an inventive experimental set-up, we studied the 3D dynamic patellar tracking in ten cadaver knees before and after valgus HTO. In each specimen, corrections of 7 degrees and 15 degrees of valgus according to, both, the OWO and CWO technique, were performed. Patellar height significantly increased with CWO and decreased with OWO. Both, OWO and CWO led to significant changes in the patellar tracking parameters tilt and rotation. We also found significant differences between OWO and CWO. Valgus high tibial osteotomy increased the medial patellar tilt and reduced the medial patellar rotation. These effects were more profound after OWO. No significant differences were found for the effect on medial-lateral patellar translation. These observations can be taken into consideration in the decision whether to perform an OWO or a CWO in a patient with medial compartment osteoarthritis of the knee.

Asymmetrical total knee arthroplasty does not improve patella tracking: a study without patella resurfacing.

It is often suggested that patella tracking after total knee arthroplasty (TKA) with an asymmetrical patella groove is more physiological than with a symmetrical patella groove. Therefore, this study tried to address two questions: what is the effect of TKA on patella tracking, and is patella tracking after asymmetrical TKA more physiological than patella tracking after symmetrical TKA? The patellar and tibial kinematics of five cadaveric knee specimens were measured in the intact situation, after the incision and suturing of a zipper, and after placement of a symmetrical TKA and an asymmetrical TKA, respectively. The patellae were not resurfaced. The flexion-extension kinematics were measured with an internal and external tibial moment to determine the envelope of motion (laxity bandwidth) of the tibio-femoral and patello-femoral articulation. The kinematics after TKA showed statistically significant changes in comparison to the intact situation: patellar medio-lateral translation, patellar tilt and tibial rotation were significantly affected. No statistically significant differences in knee kinematics were found between the symmetrical and the asymmetrical TKAs. We conclude that conventional TKA significantly changes physiological patello-femoral kinematics, and TKA with an asymmetrical patella groove does not improve the non-physiological tracking of the patella.

The trochlea is medialized by total knee arthroplasty: an intraoperative assessment in 61 patients.

BACKGROUND: A medialization of the femoral component in a total knee arthroplasty (TKA) causes abnormal patellar tracking, which could result in patellar instability, pain, wear, and failure. Previous reports defined medialization in relation to the neutral position of the femoral component, but omitted to compare it to the anatomical position of the trochlea. We assessed intraoperatively whether there is a systematic error of the position of the prosthetic groove relative to the anatomical trochlea. MATERIAL AND METHODS: A special instrument was developed to measure consecutively the mediolateral position of the anatomical trochlea and the mediolateral position of the prosthetic groove. 3 experienced knee surgeons determined the mediolateral error of the prosthetic groove in primary TKAs in 61 patients. RESULTS: There was a significant medial error of the prosthetic groove relative to the preoperative position of the trochlea, with a mean medial error of 2.5 mm (SD 3.3) INTERPRETATION: Our findings indicate that the trochlea is medialized by TKA. Because a conscious medialization of the femoral component in a TKA produces abnormal patellar tracking patterns, further investigations will be needed to analyze the clinical consequences of this medialization of the trochlea.