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Katherine Ralston - One of the best experts on this subject based on the ideXlab platform.
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Exploring changes in middle-school student lunch consumption after local school food Service Policy modifications.
Public health nutrition, 2006Co-Authors: Karen W. Cullen, Kathy Watson, Issa Zakeri, Katherine RalstonAbstract:Objective: This study assessed the impact of changes in school food Policy on student lunch consumption in middle schools. Methods: Two years of lunch food records were collected from students at three middle schools in the Houston, Texas area. During the first year, no changes occurred in the school food environment. After that school year was completed, chips and dessert foods were removed from the snack bars of all schools by the Food Service Director. Students recorded the amount and source of food and beverage items consumed. Point-of-Service purchase machines provided a day-by-day electronic data file with food and beverage purchases from the snack bars during the 2-year period. Independent t-tests and time series analyses were used to document the impact of the Policy change on consumption and sales data between the two years. Results: In general, student consumption of sweetened beverages declined and milk, calcium, vitamin A, saturated fat and sodium increased after the Policy change. Snack chips consumption from the snack bar declined in year 2; however, consumption of snack chips and candy from vending increased and the number of vending machines in study schools doubled during the study period. Ice cream sales increased significantly in year 2. Conclusions: Policy changes on foods sold in schools can result in changes in student consumption from the targeted environments. However, if all environments do not make similar changes, compensation may occur.
Simone Pettigrew - One of the best experts on this subject based on the ideXlab platform.
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Objective assessment of compliance with a state-wide school food-Service Policy via menu audits.
Public health nutrition, 2019Co-Authors: Gael Myers, Megan Sauzier, Amanda Ferguson, Simone PettigrewAbstract:Objective The Healthy Food and Drink Policy was implemented in Western Australian government schools in 2007. The aim of the present study was to assess the compliance of Western Australian school canteen menus with the Policy a decade after its introduction. Design The traffic-light system that underpins the Healthy Food and Drink Policy categorises foods and drinks into three groups: 'green' healthy items, 'amber' items that should be selected carefully and 'red' items that lack nutritional value. Canteen menus were collected online and each menu item was coded as a green, amber or red choice. Setting Western Australia.ParticipantsOnline canteen menus from 136 primary and secondary government schools. Results The majority of audited school menus met Policy requirements to include ≥60 % green items (84 %) and ≤40 % amber items (90 %), but only 52 % completely excluded red items. Overall, approximately half (48 %) of school canteen menus met all three traffic-light targets. On average, 70 % of the menu items were green, 28 % were amber and 2 % were red. Primary-school canteen menus were more likely than those from secondary schools to meet the requirements of the Policy. Conclusions While the sampled Western Australian government school canteen menus were highly compliant with most of the requirements of the Healthy Food and Drink Policy, many offered red foods and/or drinks. Providing all schools with further education about identifying red items and offering additional Services to secondary schools may help improve compliance rates.
Eui Yong Lee - One of the best experts on this subject based on the ideXlab platform.
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An optimal Service rate in a Poisson arrival queue with two-stage Service Policy*
Mathematical Methods of Operations Research (ZOR), 2003Co-Authors: Jongho Bae, Jong-woo Kim, Eui Yong LeeAbstract:We consider a two-stage Service Policy for a Poisson arrival queueing system. The idle server starts to work with ordinary Service rate when a customer arrives. If the number of customers in the system reaches N, the Service rate gets faster and continues until the system becomes empty. Otherwise, the server finishes the busy period with ordinary Service rate. After assigning various operating costs to the system, we show that there exists a unique fast Service rate minimizing the long-run average cost per unit time. Copyright Springer-Verlag 2003
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a pλm Policy for an m g 1 queueing system
Applied Mathematical Modelling, 2002Co-Authors: Jongho Bae, Sunggon Kim, Eui Yong LeeAbstract:Abstract We introduce P λ M -Service Policy for an M / G /1 queueing system. The stationary distribution of the workload under this Policy is explicitly obtained through a decomposition technique, renewal reward theorem, and level crossing argument.
Alexander L. Stolyar - One of the best experts on this subject based on the ideXlab platform.
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Multiclass multiserver queueing system in the Halfin–Whitt heavy traffic regime: asymptotics of the stationary distribution
Queueing Systems, 2012Co-Authors: David Gamarnik, Alexander L. StolyarAbstract:We consider a heterogeneous queueing system consisting of one large pool of O ( r ) identical servers, where r →∞ is the scaling parameter. The arriving customers belong to one of several classes which determines the Service times in the distributional sense. The system is heavily loaded in the Halfin–Whitt sense, namely the nominal utilization is $1-a/\sqrt{r}$ where a >0 is the spare capacity parameter. Our goal is to obtain bounds on the steady state performance metrics such as the number of customers waiting in the queue Q ^ r (∞). While there is a rich literature on deriving process level (transient) scaling limits for such systems, the results for steady state are primarily limited to the single class case. This paper is the first one to address the case of heterogeneity in the steady state regime. Moreover, our results hold for any Service Policy which does not admit server idling when there are customers waiting in the queue. We assume that the interarrival and Service times have exponential distribution, and that customers of each class may abandon while waiting in the queue at a certain rate (which may be zero). We obtain upper bounds of the form $O(\sqrt{r})$ on both Q ^ r (∞) and the number of idle servers. The bounds are uniform w.r.t. parameter r and the Service Policy. In particular, we show that $\limsup_{r} \mathbb {E}\exp(\theta r^{-{1\over2}}Q^{r}(\infty))
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multiclass multiserver queueing system in the halfin whitt heavy traffic regime asymptotics of the stationary distribution
Queueing Systems, 2012Co-Authors: David Gamarnik, Alexander L. StolyarAbstract:We consider a heterogeneous queueing system consisting of one large pool of O(r) identical servers, where r?? is the scaling parameter. The arriving customers belong to one of several classes which determines the Service times in the distributional sense. The system is heavily loaded in the Halfin---Whitt sense, namely the nominal utilization is $1-a/\sqrt{r}$ where a>0 is the spare capacity parameter. Our goal is to obtain bounds on the steady state performance metrics such as the number of customers waiting in the queue Q r (?). While there is a rich literature on deriving process level (transient) scaling limits for such systems, the results for steady state are primarily limited to the single class case. This paper is the first one to address the case of heterogeneity in the steady state regime. Moreover, our results hold for any Service Policy which does not admit server idling when there are customers waiting in the queue. We assume that the interarrival and Service times have exponential distribution, and that customers of each class may abandon while waiting in the queue at a certain rate (which may be zero). We obtain upper bounds of the form $O(\sqrt{r})$ on both Q r (?) and the number of idle servers. The bounds are uniform w.r.t. parameter r and the Service Policy. In particular, we show that $\limsup_{r} \mathbb {E}\exp(\theta r^{-{1\over2}}Q^{r}(\infty)) 0.
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multiclass multiserver queueing system in the halfin whitt heavy traffic regime asymptotics of the stationary distribution
arXiv: Probability, 2011Co-Authors: David Gamarnik, Alexander L. StolyarAbstract:We consider a heterogeneous queueing system consisting of one large pool of $O(r)$ identical servers, where $r\to\infty$ is the scaling parameter. The arriving customers belong to one of several classes which determines the Service times in the distributional sense. The system is heavily loaded in the Halfin-Whitt sense, namely the nominal utilization is $1-a/\sqrt{r}$ where $a>0$ is the spare capacity parameter. Our goal is to obtain bounds on the steady state performance metrics such as the number of customers waiting in the queue $Q^r(\infty)$. While there is a rich literature on deriving process level (transient) scaling limits for such systems, the results for steady state are primarily limited to the single class case. This paper is the first one to address the case of heterogeneity in the steady state regime. Moreover, our results hold for any Service Policy which does not admit server idling when there are customers waiting in the queue. We assume that the interarrival and Service times have exponential distribution, and that customers of each class may abandon while waiting in the queue at a certain rate (which may be zero). We obtain upper bounds of the form $O(\sqrt{r})$ on both $Q^r(\infty)$ and the number of idle servers. The bounds are uniform w.r.t. parameter $r$ and the Service Policy. In particular, we show that $\limsup_r E \exp(\theta r^{-1/2}Q^r(\infty)) 0$.
Karen W. Cullen - One of the best experts on this subject based on the ideXlab platform.
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Exploring changes in middle-school student lunch consumption after local school food Service Policy modifications.
Public health nutrition, 2006Co-Authors: Karen W. Cullen, Kathy Watson, Issa Zakeri, Katherine RalstonAbstract:Objective: This study assessed the impact of changes in school food Policy on student lunch consumption in middle schools. Methods: Two years of lunch food records were collected from students at three middle schools in the Houston, Texas area. During the first year, no changes occurred in the school food environment. After that school year was completed, chips and dessert foods were removed from the snack bars of all schools by the Food Service Director. Students recorded the amount and source of food and beverage items consumed. Point-of-Service purchase machines provided a day-by-day electronic data file with food and beverage purchases from the snack bars during the 2-year period. Independent t-tests and time series analyses were used to document the impact of the Policy change on consumption and sales data between the two years. Results: In general, student consumption of sweetened beverages declined and milk, calcium, vitamin A, saturated fat and sodium increased after the Policy change. Snack chips consumption from the snack bar declined in year 2; however, consumption of snack chips and candy from vending increased and the number of vending machines in study schools doubled during the study period. Ice cream sales increased significantly in year 2. Conclusions: Policy changes on foods sold in schools can result in changes in student consumption from the targeted environments. However, if all environments do not make similar changes, compensation may occur.
