Forecast horizon aggregation in integer autoregressive moving average (INARMA) models

This paper addresses aggregation in integer autoregressive moving average (INARMA) models. Although aggregation in continuous-valued time series has been widely discussed, the same is not true for integer-valued time series. Forecast horizon aggregation is addressed in this paper. It is shown that the overlapping forecast horizon aggregation of an INARMA process results in an INARMA process. The conditional expected value of the aggregated process is also derived for use in forecasting. A simulation experiment is conducted to assess the accuracy of the forecasts produced by the aggregation method and to compare it to the accuracy of cumulative h-step ahead forecasts over the forecasting horizon. The results of an empirical analysis are also provided

Interface Fracture in Masonry Composites: A Lattice Approach

The brick-mortar bond or interface is often the weakest link in the masonry composites. The localization of fracture processes at this bi-material interface plays an important role in the failure of this assemblage. These micro-level fracture processes control the nonlinear behavior of the brick-mortar interface which significantly affects the global behavior of the masonry structure at the continuum macro level. 2D Lattice-based micro-level fracture simulations which are based on Voronoi tessellation to discretize the continuum brick and mortar domains are applied to study progressive debonding of brick-mortar interfaces in unreinforced masonry composites. An energy method is subsequently employed to obtain the energy release rate of the lattice mesh as the crack propagates which is determined by considering the variation in the global stiffness matrix of the mesh with respect to crack length change. This energy release rate is inserted into the Irwin type fracture relationship for plane strain to calculate the modulus of complex stress intensity factor and its mode 1 and mode 2 values which are independent of the distance from the crack tip in the lattice. The lattice results for the energy release rate and stress intensity factors are then validated by comparing with three classic fracture mechanics problems analytical solutions of which are available in the literature. Afterwards, the 2-D plane strain lattice formulation is applied to simulate interfacial fracture properties of conventional test configurations in masonry. The computational lattice model is capable of evaluating the fracture toughness of brick-mortar interface along with other fracture properties from basic strength properties of lattice struts, which are removed by erosion upon failure. This information is employed to upscale the lattice fracture arguments onto the meso-level to quantify the fracture energy formulation of traction-separation cohesive zone models in the context of continuum finite element simulations of heterogeneous media such as masonry. The fracture energy from the lattice is also used in homogenizing a heterogeneous anisotropic masonry unit cell under direct tension using energy equivalence concept to obtain a scalar damage parameter which could be utilized to model the nonlinear behavior of a homogenized isotropic continuum finite element.Civil and Environmental Engineering, Department o

A Late Presentation of Spontaneous Bladder Rupture During Labor

AbstractSpontaneous bladder rupture is usually due to bladder diseases. Bladder rupture during labor or postpartum is extremely rare. Acute abdomen is the usual presentation of spontaneous bladder rupture. Patients may complain of suprapubic pain, anuria and hematuria. Some patients with intraperitoneal bladder rupture may have no abdominal pain and can pass urine without any symptoms so the diagnosis of intraperitoneal rupture may be difficult in these situations. We report a nulliparous woman with abdominal pain and distension about 20 days after normal vaginal delivery. There was intraperitoneal rupture of bladder in dome of bladder which was sealed by jejunum

Grocery omnichannel perishable inventories: performance measures and influencing factors

Purpose- Perishable inventory management for the grocery sector has become more challenging with extended omnichannel activities and emerging consumer expectations. This paper aims to identify and formalize key performance measures of omnichannel perishable inventory management (OCPI) and explore the influence of operational and market-related factors on these measures. Design/methodology/approach- The inductive approach of this research synthesizes three performance measures (product waste, lost sales and freshness) and four influencing factors (channel effect, demand variability, product perishability and shelf life visibility) for OCPI, through industry investigation, expert interviews and a systematic literature review. Treating OCPI as a complex adaptive system and considering its transaction costs, this paper formalizes the OCPI performance measures and their influencing factors in two statements and four propositions, which are then tested through numerical analysis with simulation. Findings- Product waste, lost sales and freshness are identified as distinctive OCPI performance measures, which are influenced by product perishability, shelf life visibility, demand variability and channel effects. The OCPI sensitivity to those influencing factors is diverse, whereas those factors are found to moderate each other's effects. Practical implications- To manage perishables more effectively, with less waste and lost sales for the business and fresher products for the consumer, omnichannel firms need to consider store and online channel requirements and strive to reduce demand variability, extend product shelf life and facilitate item-level shelf life visibility. While flexible logistics capacity and dynamic pricing can mitigate demand variability, the product shelf life extension needs modifications in product design, production, or storage conditions. OCPI executives can also increase the product shelf life visibility through advanced stock monitoring/tracking technologies (e.g. smart tags or more comprehensive barcodes), particularly for the online channel which demands fresher products. Originality/value- This paper provides a novel theoretical view on perishables in omnichannel systems. It specifies the OCPI performance, beyond typical inventory policies for cost minimization, while discussing its sensitivity to operations and market factors

Forecast horizon aggregation in integer autoregressive moving average (INARMA) models

This paper addresses aggregation in integer autoregressive moving average (INARMA) models. Although aggregation in continuous-valued time series has been widely discussed, the same is not true for integer-valued time series. Forecast horizon aggregation is addressed in this paper. It is shown that the overlapping forecast horizon aggregation of an INARMA process results in an INARMA process. The conditional expected value of the aggregated process is also derived for use in forecasting. A simulation experiment is conducted to assess the accuracy of the forecasts produced by the aggregation method and to compare it to the accuracy of cumulative h-step ahead forecasts over the forecasting horizon. The results of an empirical analysis are also provided

Reproducibility in forecasting research

The importance of replication has been recognised across many scientific disciplines. Reproducibility is a necessary condition for replicability, because an inability to reproduce results implies that the methods have not been specified sufficiently, thus precluding replication. This paper describes how two independent teams of researchers attempted to reproduce the empirical findings of an important paper, ‘‘Shrinkage estimators of time series seasonal factors and their effect on forecasting accuracy’’ (Miller & Williams, 2003). The two teams proceeded systematically, reporting results both before and after receiving clarifications from the authors of the original study. The teams were able to approximately reproduce each other’s results, but not those of Miller and Williams. These discrepancies led to differences in the conclusions as to the conditions under which seasonal damping outperforms classical decomposition. The paper specifies the forecasting methods employed using a flowchart. It is argued that this approach to method documentation is complementary to the provision of computer code, as it is accessible to a broader audience of forecasting practitioners and researchers. The significance of this research lies not only in its lessons for seasonal forecasting but also, more generally, in its approach to the reproduction of forecasting research

Correlation between CRP and early failure of arteriovenous fistula (AVF)

Background: Arteriovenous Fistula (AVF) is the ideal method of vascular access for patients on maintenance hemodialysis (HD). Therefore it is an important part of treatment in HD. There are several observations that indicate the role of inflammation in failure of AVF. The aim of this study was to evaluate the hematologic and inflammatory biomarkers in early AVF failure. Methods: This case-control study included 110 ESRD patients, whom were undergone AVF creation, divided in two groups. About 700 radius-cephalic AVF were created during these two years. We found 55 cases with AVF failure. In this study, we compared those 55 failures with 55 functional AVF which were selected using randomized sampling from the rest of patients according to age, gender, and AVF location. Levels of serum C-reactive protein (CRP) were checked in both groups to evaluate the relation between AVF failure and CRP level before surgery. Results: The mean±SD age of the patients was 49.7±17.28 years. CRP was positive in 34 patients (61.8) with unsuccessful fistula function, while only 4 (7.3) of those with successful AVF had positive CRP and the rest had negative CRP. The difference between the two groups of patients was strongly significant (p<0.001). Statistically, there was not any significant difference between the average of age (p: 0.580) of patients in the control and experimental groups. However, the gender (p: 0.832) discrepancies was not meaningful between the groups. Conclusion: AVF thrombosis is one of the main complications after AVF creation. Therefore, it is recommended to check CRP before AVF surgery to prevent possible failure of the fistula function