Approximation algorithms and hardness results for the joint replenishment Problepm with constant demands

19th Annual European Symposium, Saarbrücken, Germany, September 5-9, 2011. ProceedingsIn the Joint Replenishment Problem (JRP), the goal is to coordinate the replenishments of a collection of goods over time so that continuous demands are satisfied with minimum overall ordering and holding costs. We consider the case when demand rates are constant. Our main contribution is the first hardness result for any variant of JRP with constant demands. When replenishments per commodity are required to be periodic and the time horizon is infinite (which corresponds to the so-called general integer model with correction factor), we show that finding an optimal replenishment policy is at least as hard as integer factorization. This result provides the first theoretical evidence that the JRP with constant demands may have no polynomial-time algorithm and that relaxations and heuristics are called for. We then show that a simple modification of an algorithm by Wildeman et al. (1997) for the JRP gives a fully polynomial-time approximation scheme for the general integer model (without correction factor). We also extend their algorithm to the finite horizon case, achieving an approximation guarantee asymptotically equal to √9/8

Clinical characteristics differ between patients with non-traumatic neck pain, patients with whiplash-associated disorders, and pain-free individuals

BackgroundEvidence is lacking to what extent patients with Whiplash-Associated Disorders (WAD), those with non-traumatic neck pain (NTNP), and pain-free individuals differ regarding type and severity of impairments, disability, and psychological factors.Objective To compare clinical characteristics between patients with WAD, with NTNP, and pain-free individuals in primary care physiotherapy. Additionally, differences between patient groups for both acute and chronic symptoms were assessed.MethodA cross-sectional study was conducted including 168 patients with WAD, 336 matched patients with NTNP, and 336 pain-free individuals. Differences and prevalence rates were calculated for pain intensity, pain distribution, cervical range of motion, neck flexor muscle endurance, self-reported disability, and psychological factors.Results Patients with WAD had higher pain intensity (median 6/10 vs. 5/10 p83%) scored in the normal range. No significant differences between the patient groups were observed (p>.16). Both patient groups scored significantly worse than pain-free individuals on all characteristics. Patients with WAD and NTNP experienced different types of activity limitations and participation restrictions.ConclusionWAD is a more severe condition than NTNP and should be considered a separate subgroup. A different approach in clinical practice and research is required for WAD and NTNP

Clinical characteristics differ between patients with non-traumatic neck pain, patients with whiplash-associated disorders, and pain-free individuals

BackgroundEvidence is lacking to what extent patients with Whiplash-Associated Disorders (WAD), those with non-traumatic neck pain (NTNP), and pain-free individuals differ regarding type and severity of impairments, disability, and psychological factors.Objective To compare clinical characteristics between patients with WAD, with NTNP, and pain-free individuals in primary care physiotherapy. Additionally, differences between patient groups for both acute and chronic symptoms were assessed.MethodA cross-sectional study was conducted including 168 patients with WAD, 336 matched patients with NTNP, and 336 pain-free individuals. Differences and prevalence rates were calculated for pain intensity, pain distribution, cervical range of motion, neck flexor muscle endurance, self-reported disability, and psychological factors.Results Patients with WAD had higher pain intensity (median 6/10 vs. 5/10 p83%) scored in the normal range. No significant differences between the patient groups were observed (p>.16). Both patient groups scored significantly worse than pain-free individuals on all characteristics. Patients with WAD and NTNP experienced different types of activity limitations and participation restrictions.ConclusionWAD is a more severe condition than NTNP and should be considered a separate subgroup. A different approach in clinical practice and research is required for WAD and NTNP

Optimization of the charge transport in poly(phenylene vinylene) derivatives by processing and chemical modification

We present a systematic study of the influence of the processing conditions on the charge-carrier mobility in hole-only diodes and field-effect transistors (FETs) based on alkoxy-substituted poly(p-phenylene vinylene) (PPV). It is demonstrated that by chemical modification from asymmetrically to fully symmetrically substituted PPVs the mobility in both types of devices can be significantly improved. Furthermore, for symmetrical PPVs the mobility is strongly dependent on processing conditions, such as choice of solvents and annealing conditions. The increase in mobility is accompanied by a strong enhancement of the anisotropy in the charge transport. Ultimately, mobility of up to 10−2 cm2/Vs in FETs and 10−5 cm2/Vs in hole-only diodes have been achieved.