•A multi-period multi-commodity cross dock scheduling model is proposed.•The delayed loads are stored to send at the next periods.•The problem is modeled in a mixed integer linear mathematical ...model.•A heuristic algorithm is proposed to solve the model.•Product substitution is considered in a cross dock system.
Nowadays, cross docking is used as a concept to improve the response time and it reduces the inventory holding cost significantly. In some operational cases, inbound trucks leave the cross dock outbound doors in predefined departure times. In this paper, we propose an inbound truck scheduling model based on fixed outbound trucks’ departure times. Indeed, it is assumed that delayed loads are stored in temporary storage until the next outbound trucks’ departure time with the same destination. Furthermore, according to the post-distribution concept, it is assumed the other destination loads can be replaced with the delayed loads. This paper finds the best sequence of inbound trucks based on the loads substitution concept. To solve the model, a heuristic algorithm is developed and numerical tests are given to compare the results with the optimal solution. The results show using loads substitution concept will reduce cross dock holding costs until 27%.
Scheduling projects incorporated with materials ordering results in a more realistic problem. This paper deals with the combined problem of project scheduling and material ordering. The purpose of ...this paper is to minimize the total cost of this problem by determining the optimal values of activity duration, activity finish time and the material ordering schedule subject to constraints. We employ a genetic algorithm approach to solve it. Elements of the algorithm, such as chromosome structure, unfitness function, crossover, mutation and local search operations are explained. The results of the experimentation are quite satisfactory.
This paper considers the problem of a vendor-buyer integrated production-inventory model. The vendor manufactures the item at a finite rate and delivers the final goods at a lot-for-lot shipment ...policy to the buyer. We relax the assumption of uniform demand in the hitherto existing joint economic lot sizing models and analyze the problem where the end customer demand is price-sensitive. The relation between demand and price is considered to be linear. The model proposed, based on the integrated expected total relevant profits of both buyer and vendor, finds out the optimal values of order quantity and mark-up percentage, using an analytical approach. Some numerical examples are also used to analyze the effect of the price-sensitivity of demand on the improvements in joint total profit over individually derived policies.
A digital outphasing transmitter is presented for 2.4-GHz WiFi. The transmitter consists of two delay-based phase modulators and a 26-dBm integrated switching class-D power amplifier. The delay-based ...phase modulator delays incoming LO edges with a resolution of 1.4 ps (8 bit) required to meet WiFi requirements. A phase MUX architecture is proposed to implement switching between phases once every LO period (2.4 GHz) without generating detrimental glitches at the output. Due to its open-loop nature, the proposed phase modulator is capable of delivering wide OFDM bandwidths up to 40 MHz. The paper analyzes the impact of impairments, e.g., delay mismatch within the delay cells and outphasing mismatches, as well as associated mitigation techniques. The transmitter has been implemented in a 32-nm digital CMOS process and delivers an OFDM average power of 20 dBm with an overall system efficiency of 18.6% when transmitting 54-Mb/s 64QAM signal. The fully digital design is expected to further improve in power dissipation and chip-area with further CMOS scaling.
A 2.4 GHz outphasing power amplifier (PA) is implemented in a 32 nm CMOS process. An inverter-based class-D PA topology is utilized to obtain low output impedance and good linearity in the outphasing ...system. MOS switch non-idealities, such as finite on-resistance and finite rise and fall times are analyzed for their impact on outphasing linearity and efficiency. Outphasing combining is performed via a transformer configured to achieve reduced loss at power backoff. The fabricated class-D outphasing PA delivers 25.3 dBm peak CW power with 35% total system Power Added Efficiency (includes all drivers). Average OFDM power is 19.6 dBm with efficiency 21.8% when transmitting WiFi signals with no linearization required. The PA is packaged in a flip-chip BGA package. Good linearity performance (ACPR and EVM) demonstrates the applicability of inverter-based class-D amplifiers for outphasing configurations.
In this paper we focus on a two-stage supply chain consisting of one vendor and one buyer. We develop an integrated production–inventory–marketing model to determine the relevant profit-maximizing ...decision variable values. The model proposed is based on the joint total profit of both the vendor and the buyer, and it finds out the optimal ordering, shipment and pricing policies. We are able to ascertain the optimal decision variable values employing an analytical solution procedure. The numerical evidence suggests that it is more beneficial for the buyer and the vendor to cooperate with each other when the demand is more price sensitive.
Abstract Background Approximately 30% of ischemic strokes have an unknown cause. Increased atrial ectopy (AE) increases the risk of atrial fibrillation (AF), but the risk of stroke in patients with ...increased AE is unknown. Objectives This study aimed to examine whether increased AE and short atrial runs increase the risk of stroke beyond incident AF. Methods Data were collected during a 15-year follow-up of the Copenhagen Holter Study cohort with 678 men and women between 55 and 75 years of age, with no earlier history of cardiovascular disease, stroke, or AF. Study subjects underwent 48-h ambulatory electrocardiography, fasting blood tests, and clinical examination. Excessive supraventricular ectopic activity (ESVEA) was defined as the presence of either ≥30 premature atrial contractions (PACs)/hour daily or any runs of ≥20 PACs. Results Ninety-nine subjects (15%) demonstrated ESVEA. After adjusting for baseline risk factors, ESVEA was associated with ischemic stroke when censoring subjects at time of AF (hazard ratio HR: 1.96; 95% confidence interval CI: 1.10 to 3.49) or when modeling AF as a time-varying exposure (HR: 2.00; 95% CI: 1.16 to 3.45). Among subjects with ESVEA who developed a stroke, 14.3% had diagnosed AF before their stroke. The incidence of stroke in subjects with ESVEA and a CHA2 DS2 -VASc (congestive heart failure, hypertension, age 75 years or older, diabetes mellitus, previous stroke or transient ischemic attack, vascular disease, age 65 to 74 years, female) score of ≥2 was 2.4% per year, comparable to the risk observed in AF. In day-to-day analysis, ESVEA was a consistent finding. Conclusions ESVEA was associated with an increased risk of ischemic stroke beyond manifest AF in this middle-aged and older population. Stroke was more often the first clinical presentation, rather than AF, in these study subjects.
This paper shows how cognitive radio (CR) can help to optimize system power consumption of multiple input multiple output (MIMO) communication systems. Leveraging results from information theory and ...capabilities of a CR (e.g., the awareness of the component capabilities and characteristics), a theoretical framework is developed to minimize the system power consumption of MIMO systems while still considering radiated power. This paper mathematically formulates the system power consumption minimization problem under a sum rate constraint for MIMO systems. The impact of channel correlation and partial channel state information at the transmitter is considered. Numerical algorithms are developed to solve the constrained optimization problem. The simulation results show that significant power savings (e.g., up to 75% for a 4 × 4 MIMO system with Class A power amplifiers) can be achieved compared to conventional power allocation schemes. The results also show that the more computationally efficient suboptimal heuristic algorithms can achieve power savings comparable to the exhaustive search algorithm.
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