Robotic Sorting Systems: Performance Estimation and Operating Policies Analysis

Many distribution centers use expensive, conveyor-based sorting systems that require large buildings to house them. In areas with tight space, robotic sorting systems offer a new type of solution to sort parcels by destination. Such systems are highly flexible in throughput capacity and are now gradually being introduced, particularly in express companies. This paper studies robotic sorting system with two layouts. The first layout has two tiers: robots drive on the top tier and sort parcels by destination on spiral conveyors connected to roll containers at the lower tier. The second layout has a single tier with input and output points located at the perimeter, connected by robots. For each layout, we consider both the shortest path topology via dual-lane aisles and the detour path topology via single-lane aisles. We build closed queueing networks for performance estimation, design an iterative procedure to investigate robot congestion in the two-tier layout, and use a traffic flow function to estimate robot congestion in the single-tier layout. Random, closest, dedicated, and shortest-queue robot-to-loading-station assignment rules are examined. We validate analytical models by both simulation and a real case of Deppon Express and analyze the optimal system size and operating policies for throughput capacity and operating cost. The results show that the system throughput capacity is significantly affected by robot congestion in the single-tier layout with the detour path topology, but it is only slightly affected in the other systems. A square layout fits the shortest path and a rectangular layout fits the detour path. Both the random assignment rule and the shortest-queue assignment rule are superior for a large number of robots, whereas the dedicated assignment rule is superior for a small number of robots. We apply these insights at Deppon Express for different allocations in peak and off-peak hours. Our analysis shows that a robotic sorting system typically has lower overall annual cost than a traditional cross-belt sorting system when the required throughput capacity is not too large.

Peer Effects in the Adoption of a Youth Employment Subsidy

This paper studies the effects of peers on the adoption of a Youth Employment Subsidy in Chile since its inception. We examine the effects that former classmates’ and coworkers’ adoption have on one's adoption. Identification comes from discontinuities in the assignment rule that allow us to construct valid instrumental variables for peers’ adoption. Using a comprehensive set of administrative records, we find that classmates and especially coworkers play significant roles in the adoption of the subsidy. Peer effects are determined during the early stages of the program's implementation and vary by network characteristics and the strength of network ties.

Diachronic development of gender in city names in Spanish

This paper examines the gender assignment rules that apply to city names in the history of Spanish, relying for the first time on extensive corpus-based material. The empirical data show that gender assignment changed from a referential principle that consistently assigned city names to the feminine (due to the feminine basic level noun for ‘city’) to a phonologically driven assignment rule, with city names ending in -a generally being assigned to the feminine (e.g. Barcelona) and those ending in -o or -C to the masculine (e.g. Toledo, Madrid). However, the overall picture is much more complicated than previously suggested in the literature since there is still a high degree of gender variation in Modern Spanish. The use of the feminine is still possible in city names ending in -o or -C. Interestingly, the change from referential to phonological gender assignment occurs first within the NP (mainly with quantifiers such as tod- o/-a ‘all-m/-f’). It is in this morphosyntactic context that city names with final -a most commonly shift from the feminine to the masculine gender. This case of “evasive gender” will be discussed from a typological perspective.

Tone assignment and grammatical tone in Anal (Tibeto-Burman)

Complex phenomena of grammatical tone, well-described for many African languages, are increasingly attested also in the Tibeto-Burman family. This paper describes the tone assignment rule and two cases of tonal expression of grammatical categories in the Tibeto-Burman language Anal. The typologically unusual rule involves tone spreading, tonal polarity on a non-edge constituent and additional spreading, resulting in constant tonal patterns across grammatical suffixes. In two different cases the combination of the tonal pattern assigned by this rule with peculiar morpho-tonological processes results in a marking of a grammatical category (future and 1sg-person) by grammatical tone, by vowel-length, or only by the overall tonal pattern of the verbal form. Both cases are related to the omission of an explicit marking of the category, although the outcome cannot be explained only by the concept of a floating tone.

Optimizing Health and Safety Inspections in Canada

Background: Each year, the Canadian government assigns inspectors to visit firms and ensure compliance to the occupational health and safety provisions of the Canada Labour Code. This paper presents evidence supporting the hypothesis that assignments reduce the number of disabling injuries. It also presents a mathematical technique improving the performance of how firms are chosen for inspection. Methods: By combining two administrative databases covering worksites under federal jurisdiction, the impact of assignments on injuries is estimated using instrumental variables. The instruments are the exogenous part of the government’s assignment rule for inspectors. Results: The impact of one assignment on injuries is estimated to be -0.33 in the year following the assignment. Furthermore, by introducing a measure of diminishing marginal returns of assignments by sector, a more efficient assignment rule to help further minimize the number of injuries resulting from non-compliance with the Labour Code is suggested. This improved rule includes a reallocation of assignments across industries compared to the current allocation. In particular, assignments are transferred from the sectors of Air Transport and Road Transport to the sectors of Banking, Postal Contractors and Crown Corporations. Conclusions: A counterfactual experiment with the new allocation of assignments suggests an 18% decrease in the number of injuries for the same yearly average number of assignments. Based on available estimates of the cost of injuries, the suggested change in the targeting tool would lead to annual savings of 72 million dollars in workers’ compensation claims.

The Phonological Word and Stress Shift in Northern Kurmanji Kurdish

It is generally believed that stress in Kurdish is word-final. However, closer examination reveals several kinds of exceptions. This study proposes a unified analysis of regular and irregular stress patterns in Northern Kurmanji. It analyses the stress-assignment rule on the basis of a framework of prosodic phonology that divides the representation of speech into hierarchically organised units. It proposes the phonological word as the domain of stress rule and a number of other phonological processes such as glide insertion, resyllabification, vowel deletion, vowel shortening. Additionally, it proposes the cyclic analysis as the method of the rule application. Cases of stress rule violation are considered as instances of stress-shift which are conditioned by different phonological and syntactical factors or they can be accounted for by using recursive structure and phrase stress rule.

ON THE ADAN–WEISS LOSS MODEL HAVING SKILL-BASED SERVERS AND LONGEST IDLE ASSIGNMENT RULE

We consider a queueing loss system with heterogeneous skill based servers with arbitrary distributions. We assume Poisson arrivals, with each arrival having a vector indicating which of the servers are eligible to serve it. Arrivals can only be assigned to a server that is both idle and eligible. We assume arrivals are assigned to the idle eligible server that has been idle the longest and derive, up to a multiplicative constant, the limiting distribution for this system. We show that the limiting probabilities of the ordered list of idle servers depend on the service time distributions only through their means. Moreover, conditional on the ordered list of idle servers, the remaining service times of the busy servers are independent and have their respective equilibrium service distributions. We also provide an algorithm using Gibbs sampler Markov Chain Monte Carlo method for estimating the limiting probabilities and other desired quantities of this system.