Quantization noise analysis of a closed-loop PWM controller that includes Σ-Δ modulation

Σ-Δ modulation is a popular noise shaping technique which is used to move the quantization noise out of the frequency band of interest. Recently, a number of authors have applied this technique to a pulse width modulation (PWM) controller for switching power converters. However, previous analysis has not incorporated the effects of analog-to-digital converter (ADC) resolution or feedback control on the Σ-Δ modulator. In this work, quantization due to ADC resolution and PWM resolution are analyzed, considering the effects of noise-shaping and feedback. A number of simulations have been performed to explore the impact of various design choices on output noise. The study variables included the order of the Σ-Δ modulator, resolution of ADC, resolution of DPWM, the plant and the compensator. The theoretical model developed is used to generate the expected system Power Spectral Density (PSD) curves for each design choice and simulations techniques are used to validate the analysis. Experimental analysis has been performed on a digital voltage-mode control (VMC) synchronous buck converter and the output voltage PSD curves are generated using the welch method and compared with the theoretical and the simulation results. The experimental PSD curves for the 1st-order modulator match the simulation and theoretical PSD curves. This suggests that the theoretical model is a useful approximation and similar methods can be used to analyze the contribution of the quantizers to the output noise of a closed-loop controller system --Abstract, page iii

Optimisation of Flight and Maintenance Planning for Defence Aviation with Modified Artificial Bee Colony Algorithm

The planning of flight operations and maintenance is a crucial activity for both commercial and military aircraft. Military aircraft have to be always mission-ready. The task of ensuring this can become quite challenging when several operational requirements and maintenance constraints are to be fulfilled simultaneously. This paper, therefore, addresses the optimisation of flight and maintenance planning (FMP) when several diverse factors such as aircraft flying hours (AFH), flight cycles (FC), calendar life, annual flying requirement (AFR), etc. are to be factored in. Such a problem has not been considered previously. Because the problem can become unwieldy to solve by other methods, two schemes, that is, the genetic algorithm (GA) and modified artificial bee colony (ABC) algorithm for constrained optimisation have been utilised. The objective is to maximise the utilisation rate (UR) of aircraft, while also satisfying other operational and maintenance constraints. The algorithm is tested on a fleet of eight aircraft. In addition to a one-year planning period, a planning horizon of ten years has also been simulated. The results show that both the GA and modified ABC algorithm can be effectively used to solve the FMP problem

Nanoscale cuticle density variations correlate with pigmentation and color in butterfly wing scales

How pigment distribution correlates with cuticle density within a microscopic butterfly wing scale, and how both impact final reflected color remains unknown. We used ptychographic X-ray computed tomography to quantitatively determine, at nanoscale resolutions, the three-dimensional mass density of scales with pigmentation differences. By comparing cuticle densities with pigmentation and color within a scale, we determine that the lower lamina structure in all scales has the highest density and lowest pigmentation. Low pigment levels also correlate with sheet-like chitin structures as opposed to rod-like structures, and distinct density layers within the lower lamina help explain reflected color. We propose that pigments, in addition to absorbing specific wavelengths, can affect cuticle polymerization, density, and refractive index, thereby impacting reflected wavelengths that produce structural colors

Is the Deep Inspiration Breath-Hold Technique Superior to the Free Breathing Technique in Cardiac and Lung Sparing while Treating both Left-Sided Post-Mastectomy Chest Wall and Supraclavicular Regions

Aims: To evaluate the efficacy of the deep inspirational breath-hold (DIBH) technique and its dosimetric advantages over the free breathing (FB) technique in cardiac (heart and left anterior descending artery [LAD]) and ipsilateral lung sparing in left-sided post-mastectomy field-in-field conformal radiotherapy. DIBH is highly reproducible, and this study aims to find out its dosimetric benefits over FB. Materials and Methods: Nineteen left-sided mastectomy patients were immobilized using breast boards with both arms positioned above the head. All patients had 2 sets of planning CT images (one in FB and another in DIBH) with a Biograph TruePoint HD CT scanner in the same setup. DIBH was performed by tracking the respiratory cycles using a Varian Real-Time Position Management system. The target (chest wall and supraclavicular region), organs at risk (OARs; ipsilateral lung, contralateral lung, heart, LAD, and contralateral breast), and other organs of interests were delineated as per the RTOG (Radiation Therapy Oncology Group) contouring guidelines. The single-isocenter conformal fields in the field treatment plans were generated with the Eclipse Treatment Planning System (Varian Medical Systems) for both FB and DIBH images, and the doses to the target and OARs were compared. The standard fractionation regimen of 50 Gy in 25 fractions over a period of 5 weeks was used for all patients in this study. Results and Discussion: The target coverage parameters (V95, V105, V107, and Dmean) were found to be 97.8 ± 0.9, 6.1 ± 3.4, 0.2 ± 0.3, and 101.9 ± 0.5% in the FB plans and 98.1 ± 0.8, 6.1 ± 3.2, 0.2 ± 0.3, and 101.9 ± 0.4% in the DIBH plans, respectively. The plan quality indices (conformity index and homogeneity index) also showed 1.3 ± 0.2 and 0.1 for the FB plans and 1.2 ± 0.3 and 0.1 for the DIBH plans, respectively. There was a significant reduction in dose to the heart in the DIBH plans compared to the FB plans, with p values of nearly 0 for the V5, V10, V25, V30, and Dmean dosimetric parameters. The difference in ipsilateral lung doses between FB and DIBH showed statistically significant p values, and the differences in mean doses were found to be 7, 15.7, 11.8, and 10.7% for V5, V20, V30, and Dmean, respectively. There was a significant reduction in dose to the LAD in the DIBH compared to the FB plans. Conclusions: DIBH resulted in significant reductions in doses to the heart, LAD, and lungs, since with this technique there was an increase in the distance between the target and the OARs. With appropriate patient selection and adequate training, the DIBH technique is acceptable and achievable for radiotherapy to the chest, and therefore should be considered for all suitable patients, as this could result in fewer radiotherapy-related complications. However, this technique is time-consuming, since the setup is complex, results in an increased time for treatment delivery, and needs patient cooperation and technical expertise

An Analysis of Lung Cancer Screening Beliefs and Practice Patterns for Community Providers Compared to Academic Providers

Despite guidelines recommending annual low-dose computed tomography (LDCT) screening for lung cancer, uptake remains low due to the perceived complexity of initiating and maintaining a clinical program—problems that likely magnify in underserved populations. We conducted a survey of community providers at Federally Qualified Health Centers (FQHCs) in Santa Clara County, California, to evaluate provider-related factors that affect adherence. We then compared these findings to academic providers’ (APs) LDCT screening knowledge, behaviors, and attitudes at an academic referral center in the same county. The 4 FQHCs enrolled care for 80 000 patients largely of minority descent and insured by Medi-Cal. Of the 75 FQHC providers (FQHCPs), 36 (48%) completed the survey. Of the 36 providers, 8 (22%) knew screening criteria. Fifteen (42%) FQHCPs discussed LDCT screening with patients. Compared to 36 APs, FQHCPs were more concerned about harms, false positives, discussion time, patient apathy, insurance coverage, and a lack of expertise for screening and follow-up. Yet, more FQHCPs thought screening was effective (27 [75%] of 36) compared to APs (P = .0003). In conclusion, provider knowledge gaps are greater and barriers are different for community clinics caring for underserved populations compared to their academic counterparts, but practical and scalable solutions exist to enhance adoption

An Analysis of Lung Cancer Screening Beliefs and Practice Patterns for Community Providers Compared to Academic Providers

Despite guidelines recommending annual low-dose computed tomography (LDCT) screening for lung cancer, uptake remains low due to the perceived complexity of initiating and maintaining a clinical program—problems that likely magnify in underserved populations. We conducted a survey of community providers at Federally Qualified Health Centers (FQHCs) in Santa Clara County, California, to evaluate provider-related factors that affect adherence. We then compared these findings to academic providers’ (APs) LDCT screening knowledge, behaviors, and attitudes at an academic referral center in the same county. The 4 FQHCs enrolled care for 80 000 patients largely of minority descent and insured by Medi-Cal. Of the 75 FQHC providers (FQHCPs), 36 (48%) completed the survey. Of the 36 providers, 8 (22%) knew screening criteria. Fifteen (42%) FQHCPs discussed LDCT screening with patients. Compared to 36 APs, FQHCPs were more concerned about harms, false positives, discussion time, patient apathy, insurance coverage, and a lack of expertise for screening and follow-up. Yet, more FQHCPs thought screening was effective (27 [75%] of 36) compared to APs (P = .0003). In conclusion, provider knowledge gaps are greater and barriers are different for community clinics caring for underserved populations compared to their academic counterparts, but practical and scalable solutions exist to enhance adoption