RESUMEN

Herein, we investigated the distinctive scattering properties exhibited by single gold nanorods coated with palladium (AuNRs@Pd), with variations in the Pd shell thicknesses and morphologies. AuNRs@Pd were synthesized through bottom-up epitaxial Pd growth using two different concentrations of Pd precursor. These single AuNRs@Pd displayed the characteristic of subradiant and superradiant localized surface plasmon resonance peaks, characterized by a noticeable gap marked by a Fano dip. We revealed the effect of local refractive index (RI) on the subradiant and superradiant peak energies, as well as the Fano dip in the scattering spectra of AuNRs@Pd with different Pd shell thicknesses. We demonstrated the applicability of the inflection points (IFs) method on detecting peaks and dip changes across different RIs. Thin AuNRs@Pd1mM displayed more pronounced sensitivity to peak shifts in response to variations in local RIs compared to thick AuNRs@Pd2mM. In contrast, thick AuNRs@Pd2mM exhibited greater sensitivity to changes in curvature near the subradiant and superradiant peak energies rather than peak shift sensitivity across different local RIs. Moreover, the Fano dip shift was more noticeable in thick AuNRs@Pd2mM compared to thin AuNRs@Pd1mM across different local RIs. Therefore, we provided new insight into the RI sensitivity on subradiant, superradiant, and Fano resonance modes in single AuNRs@Pd.

RESUMEN

Mathematical models may aid researchers in describing biological processes, like growth, in animals. This study aimed to collect the body weight data of 18 Boer goat castrates and 20 Boer goat does, from birth until maturity, to model growth and determine growth trends. This is a novel investigation as sufficient information on an age-weight database for these two Boer goat sexes from birth to maturity, is lacking. Using age-weight data, four nonlinear models, namely the Brody, Gompertz, Logistic and Von Bertalanffy growth models, were plotted and evaluated. The model parameters of each growth model were compared for differences between the two sexes. The statistical effectiveness of fit was determined for each model using AIC and RMSE, with R2 also being considered. All models except the Brody model, predicted significantly heavier mature weights for castrates. The Brody model was deemed unfit to describe Boer goat growth as the function severely over-predict weights from birth until maturity for both sexes. The Von Bertalanffy (R2 = 91.3) and Gompertz functions (R2 = 91.3) showed the best fit for Boer goat castrates, while the Gompertz model (R2 = 95.1) showed the best fit for Boer goat does. The Gompertz function is the preferred model to depict Boer goat growth overall, as it accurately characterized growth of both sexes. According to the Gompertz model the age at which the inflection point of the growth curve was reached, did not differ significantly between castrates and does (141.80 days versus 136.31 days). There was also no significant difference in maturation rate between the two sexes.

Asunto(s)

RESUMEN

How to distinguish and quantify past human impacts on vegetation is a significant challenge in paleoecology. Here, we propose a novel method, the error inflection point-discriminant technique. It finds out the inflection points (IPs) of the regression errors of pollen-climate transfer functions using modern pollen spectra from vegetation with different values of the Human Influence Index (HII), which represent the HII threshold values of native/secondary and secondary/artificial vegetation systems. Our results show that the HII value at the native/secondary vegetation IPs is approximately 22 and globally uniform, whereas it varies regionally for the secondary/artificial vegetation IPs. In a case study of the Liangzhu archaeological site in the lower Yangtze River, discriminant functions for pollen spectra from three vegetation types and pollen-climate transfer functions of the native vegetation were established to reconstruct paleovegetation and paleoclimate over the past 6,600 years. Our study demonstrates this method's feasibility for quantitatively distinguishing human impacts on paleovegetation and assessing quantitative paleoclimate reconstructions using pollen data.

RESUMEN

What is already known about this topic?: Previous studies have predominantly examined the micro-level aspects of women aging inflection points, while macro-level research using big data on the inflection points of aging among middle-aged and elderly women in China is currently limited. What is added by this report?: This study determined the inflection ages for physiological, psychological, social, and total dimensions in middle-aged, young elderly, and elderly women [(48.0-53.2) vs. (66.3-70.0) vs. (78.4-81.2) years old]. What are the implications for public health practice?: This study is important for gaining a deeper understanding of aging, identifying patterns of aging, and implementing targeted interventions to promote the overall health of Chinese women.

RESUMEN

Vitamin D deficiency is a global public health concern that provokes bone demineralization and weakening. In response to the decreased vitamin D level, calcium stores wear out. The homeostatic effect of compensatory hyperparathyroidism in vitamin D deficiency incites variable discrepancies in different populations. This study intends to decipher the transition point of PTH in relation to levels of vitamin D in a Nepalese population. A cross-sectional study was carried out at Tribhuvan University Teaching Hospital, Nepal. Serum calcium, phosphorus, intact PTH, and 25-hydroxy vitamin D levels were assayed in an Abbott ARCHITECT Integrated System. A correlation plot of PTH and vitamin D was analyzed in Statistical Package for Social Sciences version 22.0. Using a locally weighted scatter plot smoothing method, the relation between these variables was presented graphically. Among 281 individuals, 30.2% had vitamin D levels below 20 ng/mL. There was an archetypical transition in the PTH levels in concert with the decrease in vitamin D level marked by 2 inflection points (ie, 18.5 and 42.0 ng/mL). Our findings suggest that to augment overall health and avert weakness due to vitamin D deficiency, the levels of vitamin D should be maintained above 42.0 ng/mL in our population.

RESUMEN

BACKGROUND: Although the development of atrial fibrillation (AF) and the progression of chronic kidney disease are known to be interrelated, it remains unclear when and how renal function changes during the clinical course of AF. METHODS: This study retrospectively enrolled 131 patients who were able to collect data on estimated glomerular filtration rate (eGFR) at least five times during the 500 days before and 500 days after the first visit (baseline) of new-onset AF, respectively. To investigate the temporal relationship between the development of AF and the beginning of worsening renal function (WRF), a piecewise regression model was applied to the eGFR time series data. The time point at which the slopes of the two regression lines changed (inflection -point), the slope before and after the inflection-point (ß1 and ß2, respectively), and the difference in slope (Δß) were estimated. The presence of WRF was defined as having the inflection-point at which both Δß and ß2 were < - 0.0083 mL/min/1.73 m2/day (corresponding to 3.03 mL/min/1.73 m2/year), and the corresponding the inflection-point was defined as the beginning of WRF. RESULTS: WRF was detected in 54 (41.2%) patients. The beginning of WRF were distributed at various times, but most frequently (23 of 54 patients) within 100 days before and after baseline. The presence of WRF was not associated with age, heart failure, or baseline eGFR, but was associated with positive ß1 (odds ratio 30.5, 95% confidence interval 11.1-83.9, P < 0.01). CONCLUSION: In nearly half of AF patients with WRF, the beginning of WRF was observed within a few months before or after the first visit for AF. Patients with a positive eGFR slope before the onset of AF are more likely to develop WRF after the onset of AF, suggesting that potential kidney damage may be underlying.

Asunto(s)

RESUMEN

Aim: This article aimed to present the salient features of the in-house developed Java program for the determination of inflection point and dosimetric parameters of flattening filter-free (FFF) photon beam. Reference levels for the dosimetric parameters of the FFF photon beams were also presented. Materials and Methods: Beam profiles of 6 MV FFF and 10 MV FFF photon beams for a collimator setting of 20 cm × 20 cm measured at 10 cm depth in an isocentric setup acquired from various institutions were analyzed using an in-house developed Java program and manual method. The values of reference dose value (RDV), field size, penumbra, and degree of un-flatness (defined as the lateral separation between 90% [X90%], 75% [X75%], and 60% [X60%] dose points on the profile) were calculated and compared. The reference values of field size, penumbra, and degree of un-flatness were also determined for Varian and Elekta medical electron linear accelerators (LINACs). Results: The maximum differences for RDV determined using the Java method and manual method are 2.4% and 2.7% for 6 and 10 MV FFF photon beams, respectively. The maximum difference between the values of field size, penumbra, and degree of un-flatness determined using Java and manual methods is within 1.3 mm. The reference values of field size and penumbra for Varian LINACs are 19.94 ± 0.10 cm and 0.83 ± 0.08 cm (6 MV FFF) and 19.95 ± 0.10 cm and 0.83 ± 0.08 cm (10 MV FFF). Similarly, the reference values of field size and penumbra for Elekta LINACs are 20.02 ± 0.09 cm and 0.94 ± 0.12 cm (6 MV FFF) and 20.03 ± 0.11 cm and 0.97 ± 0.16 cm (10 MV FFF). Conclusions: A software program was developed in Java for analyzing the beam profiles of FFF photon beams. The results of Java-derived values of dosimetric parameters of FFF photon beams were found in good agreement with the values determined using the manual method. The reference values of these parameters were also derived and quoted using a large cohort of the data.

RESUMEN

Treatment of wastewater and reuse of purified water in an industrial process can provide an alternative source of fresh water as well as reduce pollution load by discharging a lower quantity of wastewater. When adsorption is used for treatment, the regeneration of the used adsorbent may also account for a large portion of the operational cost and cause secondary pollution. This problem may be solved by cyclic repetition of adsorption/regeneration cycles using a column method. In this paper, a total of nine successive cycles of zinc capture and zeolite bed regeneration using a column method have been investigated. The derived form of the breakthrough curve was used for analysing mass transfer in the column. For that purpose, the Dose-response, the Thomas, the Bohart-Adams, the Yoon-Nelson and the Wolborska models were used for modelling the breakthrough curve by nonlinear regression analysis. Simulation results and mathematical similarities between the models were discussed. This is the first study that used derived form of Dose-response model to analyse the inflection points of the breakthrough curve and mass transfer during nine consecutive sorption-regeneration cycles of zinc ions on natural zeolite. Obtained peak shape rate profiles were analysed for all cycles. Optimal operation conditions were evaluated with respect to the inflection point, the model parameters, and the residence time.

RESUMEN

PURPOSE: The aims of this study were to explore the correlations between thoracic kyphosis (TK) and lumbar lordosis (LL) parameters and to build corresponding linear regressions to predict TK morphology and the thoracolumbar inflection point (IP) determined by individual LL parameters in asymptomatic adults. METHODS: A total of 280 adult healthy volunteers were recruited, and full-spine X-rays were performed for each subject in a standing posture. The following sagittal parameters were measured: cumulative TK, LL, proximal LL (PLL), the apices of TK (TKA) and LL (LLA), the IP and the distance from the plumb line of the thoracic apex (TAPL) and the lumbar apex (LAPL) to the gravity line. The correlations between TK and LL parameters were analyzed, and the corresponding linear regressions were conducted. RESULTS: Extensive variations existed in TK alignment, including angular and morphological parameters. In addition, there were statistical correlations of all cumulative TK angles with LL (r values from - 0.173 to - 0.708) and PLL (r values from - 0.206 to - 0.803), TKA and IP with LLA (rs = 0.359 and 0.582, respectively) and TAPL with LAPL (rs = 0.335). The common predictive formulas employed in ASD surgery could include T10-L1 = - 3.6-0.2*LL (R2 = 0.201), T4-L1 = 3.4-0.5*LL (R2 = 0.457), TKA = - 10.3 + 1.1*LLA (R2 = 0.180) and IP = - 12.7 + 1.6*LLA (R2 = 0.330). CONCLUSION: There were intimate associations between TK and LL parameters in asymptomatic adults. Moreover, predictive models for thoracic alignment, particularly cumulative TK, based on LL parameters were proposed, which could better delineate anatomical relationships, guide thoracic construction during adult spinal deformity surgery and may help preventing proximal junctional failure.

RESUMEN

The multi-objective particle swarm optimization algorithm has several drawbacks, such as premature convergence, inadequate convergence, and inadequate diversity. This is particularly true for complex, high-dimensional, multi-objective problems, where it is easy to fall into a local optimum. To address these issues, this paper proposes a novel algorithm called IMOPSOCE. The innovations for the proposed algorithm mainly contain three crucial factors: 1) an external archive maintenance strategy based on the inflection point distance and distribution coefficient is designed, and the comprehensive indicator (CM) is used to remove the non-dominated solutions with poor comprehensive performance to improve the convergence of the algorithm and diversity of the swarm; 2) using the random inertia weight strategy to efficiently control the movement of particles, balance the exploration and exploitation capabilities of the swarm, and avoid excessive local and global searches; and 3) offering different flight modes for particles at different levels after each update to further enhance the optimization capacity. Finally, the algorithm is tested on 22 typical test functions and compared with 10 other algorithms, demonstrating its competitiveness and outperformance on the majority of test functions.

RESUMEN

In item response theory (IRT) modeling, the magnitude of the lower and upper asymptote parameters determines the degree to which the inflection point shifts above or below P = 0.50. The current study examines the one-parameter negative log-log model (NLLM), which is characterized by a downward shift in the inflection point, among other distinctive psychometric properties. After detailing the statistical foundations of the NLLM, we present a series of simulation studies to establish item and person parameter estimation accuracy and to demonstrate that this parsimonious model addresses the "slipping" effect (i.e., unexpectedly incorrect answers) via an inflection point < 0.50 rather than through computationally difficult estimation of the upper asymptote. We then provide further support for these simulation results through empirical data analysis. Finally, we discuss how the NLLM contributes to recent methodological literature on the utility of asymmetric IRT models.

RESUMEN

STUDY DESIGN: Prospective cohort study. OBJECTIVES: To show population variance in the Inflection Point (IP) and its role in defining maximum Thoracic Kyphosis (TK) and Lumbar Lordosis (LL). METHODS: 468 asymptomatic adult volunteers were included in the Multi-Ethnic Normative Alignment Study (MEANS). To find parameters correlating with IP, the vertebrae and discs were numbered such that C7 was 0, T1 was 1, with T1-T2 disc being 1.5, etc. Statistical analysis was performed by a correlation matrix for IP and the 9 other selected parameters along with linear regressions. RESULTS: The overall mean IP was 12.44 approximately corresponding to T12-L1 disc with the median being 12.50, range was T8-L4. The cohort was then stratified by sex and ethnicity, but there was no significant difference in IP between groups. IP in younger subjects was 13 (L1), compared to 12.5 (T12-L1 disc) in older subjects (P < .05). IP was moderately correlated with the TK apex (r = .66). No strong correlation was found between IP and LL magnitude or apex, TK magnitude, sacral slope, or Pelvic Incidence (PI). In terms of other sagittal parameters, PI and LL demonstrated a significant positive correlation. PI and TK did not have a strong association. CONCLUSIONS: The mean IP was at the T12-L1 disc, however IP ranged from T8 to L4. Older subjects tended to have a relatively more cephalad IP. No radiographic variable was found to be a strong predictor of the IP. TK apex was found to have a moderate correlation.

RESUMEN

An improved Dijkstra algorithm based on adaptive resolution grid (ARG) is proposed to assist manual transmission line planning, shorten the construction period and achieve lower cost and higher efficiency of line selection. Firstly, the semantic segmentation network is used to change the remote sensing image into a ground object-identification image and the grayscale image of the ground object-identification image is rasterized. The ARG map model is introduced to greatly reduce the number of redundant grids, which can effectively reduce the time required to traverse the grids. Then, the Dijkstra algorithm is combined with the ARG and the neighborhood structure of the grid is a multi-center neighborhood. An improved method of bidirectional search mechanism based on ARG and inflection point-correction is adopted to greatly increase the running speed. The inflection point-correction reduces the number of inflection points and reduces the cost. Finally, according to the results of the search, the lowest-cost transmission line is determined. The experimental results show that this method aids manual planning by providing a route for reference, improving planning efficiency while shortening the duration, and reducing the time spent on algorithm debugging. Compared with the comparison algorithm, this method is faster in running speed and better in cost saving and has a broader application prospect.

Asunto(s)

RESUMEN

BACKGROUND: Many factors contribute to the risk of surgical-site infection (SSI) following total shoulder arthroplasty (TSA). Operative time is a modifiable factor that may contribute to SSI occurrence after TSA. This study aimed to determine the correlation between operative time and SSI following TSA. MATERIALS AND METHODS: By use of the American College of Surgeons National Surgical Quality Improvement Program database, a total of 33,987 patient records were queried from 2006 to 2020 and sorted by operative time and the development of an SSI in the 30-day postoperative period. Odds ratios for the development of an SSI were calculated based on operative time. RESULTS: An SSI developed in the 30-day postoperative period in 169 of the 33,470 patients in this study, resulting in an overall SSI rate of 0.50%. A positive correlation was identified between operative time and the SSI rate. An inflection point was identified at an operative time of 180 minutes, with a significant increase in the rate of SSI occurrence for operative times >180 minutes. DISCUSSION AND CONCLUSION: Increased operative time was shown to be strongly correlated with an increased risk of SSI within 30 days following surgery, with a significant inflection point at 180 minutes. The target operative time for TSA should be <180 minutes to reduce the risk of SSI.

RESUMEN

Background: Previous studies have shown that serum albumin is associated with prostate cancer (PCa), but not with prostate-specific antigen (PSA) levels in populations without PCa history. Therefore, we analyzed secondary data provided by the National Health and Nutrition Examination Survey (NHANES) (2003-2010). Methods: In total, 5,469 participants were selected from the NHANES database (2003-2010). Serum albumin and PSA levels were serially considered independent and dependent variables, serially. A number of covariates were included in this study, including demographic, dietary, physical examination, and comorbidity data. Using weighted linear regression model and smooth curve fitting, the linear and non-linear relationship between serum albumin and PSA was investigated. Results: After modulating underlying interference factors, the weighted multivariate linear regression analysis revealed that serum albumin did not independently predict PSA levels (ß = -0.009 95%CI: -0.020, 0.002). Nevertheless, a non-linear relationship was found between serum albumin and PSA, with a point of 41 g/L. Left of the inflection point, the effect size, 95%CI, and P-value were 0.019 (log2 transformation) (-0.006, 0.043) and 0.1335, respectively. We found a negative association between serum albumin and PSA on the right side of the inflection point, with effect size, 95%CI, and a P-value of -0.022 (log2 transformation) (-0.037, -0.007), 0.0036. Conclusion: In summary, serum albumin and PSA levels are not linearly related. When serum albumin levels exceed 41 g, serum albumin levels are negatively associated with PSA levels.

Asunto(s)

RESUMEN

Background Understanding the natural history of elevated blood pressure (BP) is important to determine the window for primary prevention of hypertension. The authors aimed to investigate the natural history of elevated BP and examine whether there were inflection points in BP trajectories preceding hypertension onset in Chinese adults. Methods and Results A total of 8688 participants with an average of 5 BP measurements were included from the CHNS (China Health and Nutrition Survey). In each wave, triplicate measurements on the same arm were taken, and the mean systolic BP (SBP) and diastolic BP (DBP) were used in the analysis. Hypertension onset was defined as SBP ≥140 mm Hg or DBP ≥90 mm Hg or diagnosed by physician or currently under antihypertensive treatment. The median follow-up time was 13.0 years. Overall, BP elevation with age prior to the onset of hypertension showed a nonlinear trajectory. The increased rates in both SBP and DBP were obviously faster after the inflection point than before. According to hypertension onset at age 30 to 39, 40 to 49, 50 to 59, 60 to 69, and 70 to 79 years, at the inflection point, patients were ≈29, 38, 48, 57, and 67 years, SBP levels were 112.6, 114.8, 116.8, 117.4, and 118.0 mm Hg, and DBP levels were 73.4, 75.7, 76.9, 76.2, and 73.8 mm Hg, respectively. Conclusions There was a nonlinear trajectory of BP elevation preceding hypertension onset. The inflection points for SBP and DBP were in the range of 112 to 118 mm Hg and 73 to 77 mm Hg, respectively. Once BP levels exceeded the changing points, the level of SBP and DBP increased more rapidly.

Asunto(s)

RESUMEN

The demand for carbon peaking and 'carbon neutrality' is putting pressure on some provinces in central China that are on the rise in economic development and rely on coal as their main energy source. This article takes Jiangxi Province as an example to study the relationship between net CO2 emissions and 11 indicators, the STIRPAT model is used to perform multivariate linear fitting. The results of regression are used to calculate the peak value of net CO2 emissions under different scenarios, and the fuzzy set qualitative analysis method is used to study the development model of net CO2 emissions in Jiangxi Province and its control path. The results showed that: (1) Per capita GDP has the most significant impact on the net CO2 emissions, while the proportion of total forestry output value, energy conservation, environmental protection expenditures in public expenditures, the number of buses vehicles operating per 10,000 people are negatively correlated with net CO2 emissions. (2) After simulating the possible development scenarios of Jiangxi Province, it can be concluded that there are in three scenarios the net CO2 emissions are most likely to peak before 2030. (3) Configuration analysis results showed that if Jiangxi Province wants to achieve 'carbon neutrality' in 2060, it is necessary to maintain both economic structural adjustment and energy consumption structural adjustment, with carbon intensity reduction as the main goal development model. (4) The central China should give more play to the advantages of the forestry industry and strengthen the energy structure regulation policy.

Asunto(s)

RESUMEN

STUDY DESIGN: A retrospective radiologic study. OBJECTIVE: The inflection point is the disc space between a lordotic and kyphotic segment of spine. To our knowledge, there has been no study evaluating changes in functional sagittal alignment determined by inflection points after cervical fusion surgery. The purpose is to identify changes in functional sagittal alignment after cervical fusion as determined by functional segments between cervicothoracic and thoracolumbar inflection points. METHODS: Standing radiographs of the sagittal whole spine were taken in 62 patients who underwent cervical fusion procedures. We identified cervicothoracic and thoracolumbar inflection points in the sagittal plane and measured Cobb angles of resulting "functional" cervical, thoracic, and lumbar segments. We also measured the C2 and T1 sagittal vertical axis (SVA) distance to S1 and the anatomic cervical lordosis, thoracic kyphosis, lumbar lordosis, spinopelvic parameters, and T1 sagittal slope. We compared the pre- and post-op values. RESULTS: The functional cervical segment and T1 sagittal slope increased postoperatively. C2 and T1 SVA distance to S1 decreased postoperatively. In patients with a single level fusion or lower instrumented vertebra (LIV) proximal or equal to C6, functional cervical segment, and anatomic cervical lordosis increased postoperatively. In those with multiple level fusion or LIV distal or equal to C7, the C2 SVA distance to S1 decreased postoperatively. CONCLUSIONS: After cervical fusion surgery, functional cervical sagittal parameters determined by the inflection point improve without changes in the anatomic sagittal parameters. Postoperative changes in functional sagittal parameters were affected by the number of fused levels and LIV.

RESUMEN

Objective: The main aim of this study was to comprehensively explore the relationship among pelvic incidence (PI), inflection point (IP), and apex of lumbar lordosis (LLA), and establish a predictive formula for LLA based on individual PI and IP in asymptomatic Chinese adults. Methods: A total of 385 asymptomatic adults with average age 38.3 ± 11.9 years (range 20-73 years) were recruited between November 2020 and October 2021. Full-spine, standing x-rays were then obtained from each participant. Next, the following sagittal parameters were measured: PI, IP, LLA, the horizontal offset between the plumb line of the lumbar apex and that of the posterosuperior corner of S1 (LASO), the upper lumbar lordosis (ULL) and lower lumbar lordosis (LLL), lumbar lordosis (LL), and thoracic kyphosis (TK). Moreover, the association among PI, IP, and the other sagittal parameters was evaluated, followed by linear regression analyses. A P-value of <0.05 was considered statistically significant. Results: PI showed statistically significant correlations with LLA (rs = -0.629; P < 0.01), LASO (rs = 0.537; P < 0.01), LLL (rs = 0.788; P < 0.01), and LL (rs = 0.663; P < 0.01). On the other hand, IP also showed statistically significant correlations with LLA (rs = 0.671; P < 0.01), LASO (rs = -0.493; P < 0.01), LLL (rs = -0.402; P < 0.01), and LL (rs = -0.283; P < 0.01). The corresponding predictive formulae were displayed as follows: LLA = -0.03 * PI + 0.23 * IP + 14.45 (R 2 = 0.669); LASO = 0.38 * PI-2.09 * IP + 53.62 (R 2 = 0.460); and LLL = 0.58 * PI-0.88 * IP + 18.86 (R 2 = 0.659). Conclusion: The specific lumbar shape should be modulated by pelvic morphology and IP level. In addition, we established predictive formulae for ideal sagittal lumbar profile based on individual PI and IP, with the overarching goal of helping surgeons to better comprehend the regulatory mechanisms of the individual sagittal lumbar alignment, and design a precise and personalized corrective plan.

RESUMEN

Let n measurements of a process be provided sequentially, where the process follows a sigmoid shape, but the data have lost sigmoidicity due to measuring errors. If we smooth the data by making least the sum of squares of errors subject to one sign change in the second divided differences, then we obtain a sigmoid approximation. It is known that the optimal fit of this calculation is composed of two separate sections, one best convex and one best concave. We propose a method that starts at the beginning of the data and proceeds systematically to construct the two sections of the fit for the current data, step by step as n is increased. Although the minimization calculation at each step may have many local minima, it can be solved in about O ( n 2 ) operations, because of properties of the join between the convex and the concave section. We apply this method to data of daily Covid-19 cases and deaths of Greece, the United States of America and the United Kingdom. These data provide substantial differences in the final approximations. Thus, we evaluate the performance of the method in terms of its capabilities as both constructing a sigmoid-type approximant to the data and a trend detector. Our results clarify the optimization calculation both in a systematic manner and to a good extent. At the same time, they reveal some features of the method to be considered in scenaria that may involve predictions, and as a tool to support policy-making. The results also expose some limitations of the method that may be useful to future research on convex-concave data fitting.