36 research outputs found
Crowdsourced Delivery with Drones in Last Mile Logistics
We consider a combined system of regular delivery trucks and crowdsourced drones to provide a technology-assisted crowd-based last-mile delivery experience. We develop analytical models and methods for a system in which package delivery is performed by a big truck carrying a large number of packages to a neighborhood or a town in a metropolitan area and then assign the packages to crowdsourced drone operators to deliver them to their final destinations. A combination of heuristic algorithms is used to solve this NP-hard problem, computational results are presented, and an exhaustive sensitivity analysis is done to check the influence of different parameters and assumptions
On the exact solution of the no-wait flow shop problem with due date constraints
Peer ReviewedThis paper deals with the no-wait flow shop scheduling problem with due date constraints. In the no-wait flow shop problem, waiting time is not allowed between successive operations of jobs. Moreover, the jobs should be completed before their respective due dates; due date constraints are dealt with as hard constraints. The considered performance criterion is makespan. The problem is strongly NP-hard. This paper develops a number of distinct mathematical models for the problem based on different decision variables. Namely, a mixed integer programming model, two quadratic mixed integer programming models, and two constraint programming models are developed. Moreover, a novel graph representation is developed for the problem. This new modeling technique facilitates the investigation of some of the important characteristics of the problem; this results in a number of propositions to rule out a large number of infeasible solutions from the set of all possible permutations. Afterward, the new graph representation and the resulting propositions are incorporated into a new exact algorithm to solve the problem to optimality. To investigate the performance of the mathematical models and to compare them with the developed exact algorithm, a number of test problems are solved and the results are reported. Computational results demonstrate that the developed algorithm is significantly faster than the mathematical models
A Divide and Conquer Approximation Algorithm for Partitioning Rectangles
Given a rectangle with area and a set of areas
with , we consider the problem of partitioning into
sub-regions with areas in a way that the total
perimeter of all sub-regions is minimized. The goal is to create square-like
sub-regions, which are often more desired. We propose an efficient
--approximation algorithm for this problem based on a divide and conquer
scheme that runs in time. For the special case when the
aspect ratios of all rectangles are bounded from above by 3, the approximation
factor is . We also present a modified version of out
algorithm as a heuristic that achieves better average and best run times
Space Partitioning Schemes and Algorithms for Generating Regular and Spiral Treemaps
Treemaps have been widely applied to the visualization of hierarchical data.
A treemap takes a weighted tree and visualizes its leaves in a nested planar
geometric shape, with sub-regions partitioned such that each sub-region has an
area proportional to the weight of its associated leaf nodes. Efficiently
generating visually appealing treemaps that also satisfy other quality criteria
is an interesting problem that has been tackled from many directions. We
present an optimization model and five new algorithms for this problem,
including two divide and conquer approaches and three spiral treemap
algorithms. Our optimization model is able to generate superior treemaps that
could serve as a benchmark for comparing the quality of more computationally
efficient algorithms. Our divide and conquer and spiral algorithms either
improve the performance of their existing counterparts with respect to aspect
ratio and stability or perform competitively. Our spiral algorithms also expand
their applicability to a wider range of input scenarios. Four of these
algorithms are computationally efficient as well with quasilinear running times
and the last algorithm achieves a cubic running time. A full version of this
paper with all appendices, data, and source codes is available at
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Approximating Median Points in a Convex Polygon
We develop two simple and efficient approximation algorithms for the
continuous -medians problems, where we seek to find the optimal location of
facilities among a continuum of client points in a convex polygon with
vertices in a way that the total (average) Euclidean distance between
clients and their nearest facility is minimized. Both algorithms run in
time. Our algorithms produce solutions within a
factor of 2.002 of optimality. In addition, our simulation results applied to
the convex hulls of the State of Massachusetts and the Town of Brookline, MA
show that our algorithms generally perform within a range of 5\% to 22\% of
optimality in practice
Increasing Supply Chain Resiliency Through Equilibrium Pricing and Stipulating Transportation Quota Regulation
Supply chain disruption can occur for a variety of reasons, including natural
disasters or market dynamics for which resilient strategies should be designed.
If the disruption is profound and with dire consequences for the economy, it
calls for the regulator's intervention to minimize the impact for the
betterment of the society. This paper considers a shipping company with limited
capacity which will ship a group of products with heterogeneous transportation
and production costs and prices, and investigates the minimum quota regulation
on transportation amounts stipulated by the government. An interesting example
can happen in North American rail transportation market, where the rail
capacity is used for a variety of products and commodities such as oil and
grains. Similarly, in Europe supply chain of grains produced in Ukraine is
disrupted by the Ukraine war and the blockade of sea transportation routes,
which puts pressure on rail transportation capacity of Ukraine and its
neighboring countries to the west that needs to be shared for shipping a
variety of products including grains, military, and humanitarian supplies. Such
situations require a proper execution of government intervention for effective
management of the limited transportation capacity to avoid the rippling effects
throughout the economy. We propose mathematical models and solutions for the
market players and the government in a Canadian case study. Subsequently, the
conditions that justify government intervention are identified, and an
algorithm to obtain the optimum minimum quotas is presented
The feasibility of creating a natural habitat for spawning, bony fish in the Caspian Sea in order to preserve biodiversity and genetic risk
The purpose of this study was to investigate the possibility of natural reproduction of indanger fish in the southern Caspian Sea in Tajan, Haraz,Sardabrood and Chalos rivers, and identify suitable habitats for this species in the study area as a genetic reserve.Sampling of physical and chemical parameters of water, macrobenthic invertebrates and fish fauna was conducted seasonaly in each rivers at selected stations from febrary 2010 during one year. Macrobenthic invertebrate sampling were used bySorber sampler and fish was collected by gill net and electroshocker set with a voltage of 1.7 A and 100-300 V. A total of 53 taxa of macrobenticinvertabrateshave been identified in the four mentioned rivers, in which Tajanriverconsisted of 47 taxa with highest richness.20 species of fish were determined in the studied rivers that 6 of them were non-native species.The results showed that the predominant identified fish species were native in the river. The fish species diversity increases as one moves from the headstream towards the estuaries of the two studied Sardabrud and Chalus rivers.The results of this study showed that the relative abundance of fish species resistant to pollution and hard environmental conditions were much more that sensitive species. physicochemical parameters of water such as; water temperature, DO, BOD5, pH, TSS, TDS, EC, turbidity, nutrients, biodiversity index such as Shanon index, EPT, HFBI, EPT/CHIR, nutrition functioning group and present or absent of fish species showed that there are significant decrease in water qualities from upstraem ratio to down stream (For example, in Tajan river water turbidity varied from 0 at station 1 to 333 NTU at station 6, Which is strongly influenced by sand workshops. As well as the activities of a significant impact of fish farming workshop on the Haraz river water quality). The minimum of HFBI index was 2.84 at station 1 and the maximum was recorded at station 5 with 6.01, and there is not any possibility to natural reproduction of migrated species that are dominant and indanger at downstream. Conditions for natural reproduction of this species in the rivers of srdabrood and Chalus there is to some. In Shahid- Rajaei dam the maximum relative abundance of fish species belonged to Capoeta capoeta, Luciobarbus capito and Squalius cephalus, respectively. These species have different age, length and weight stuctures at Shahid- Rajaei dam inhabitant, and the resourval of this dam and it,s upstream have been preparing auch a favorabile condition that seems there are potentioal of introductionand inhabitant of some of the Migratory and indanger fish species such as Barbels, Sturgeon, Alburnus chalcoides and etc. as genetic reserve for biodiversity preservation
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Measuring the Conditional Luminosity and Stellar Mass Functions of Galaxies by Combining the Dark Energy Spectroscopic Instrument Legacy Imaging Surveys Data Release 9, Survey Validation 3, and Year 1 Data
In this investigation, we leverage the combination of the Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys Data Release 9, Survey Validation 3, and Year 1 data sets to estimate the conditional luminosity functions and conditional stellar mass functions (CLFs and CSMFs) of galaxies across various halo mass bins and redshift ranges. To support our analysis, we utilize a realistic DESI mock galaxy redshift survey (MGRS) generated from a high-resolution Jiutian simulation. An extended halo-based group finder is applied to both MGRS catalogs and DESI observation. By comparing the r- and z-band luminosity functions (LFs) and stellar mass functions (SMFs) derived using both photometric and spectroscopic data, we quantified the impact of photometric redshift (photo-z) errors on the galaxy LFs and SMFs, especially in the low-redshift bin at the low-luminosity/mass end. By conducting prior evaluations of the group finder using MGRS, we successfully obtain a set of CLF and CSMF measurements from observational data. We find that at low redshift, the faint-end slopes of CLFs and CSMFs below ∼109 h −2 L ⊙ (or h −2 M ⊙) evince a compelling concordance with the subhalo mass functions. After correcting the cosmic variance effect of our local Universe following Chen et al., the faint-end slopes of the LFs/SMFs turn out to also be in good agreement with the slope of the halo mass function