43 research outputs found
A Neighborhood Search and Set Cover Hybrid Heuristic for the Two-Echelon Vehicle Routing Problem
The Two-Echelon Vehicle Routing Problem (2E-VRP) is a variant of the classical vehicle routing problem arising in the context of city logistics. In the 2E-VRP, freight from a main depot is delivered to final customers using intermediate facilities, called satellites. In this paper, we propose a new hybrid heuristic method for solving the 2E-VRP that relies on two components. The first component effectively explores the search space in order to discover a set of interesting routes. The second recombines the discovered routes into high-quality solutions. Experimentations on benchmark instances show the performance of our approach: our algorithm achieves high-quality solutions in short computational times and improves the current best known solutions for several large scale instances
Prompt Problems: A New Programming Exercise for the Generative AI Era
Large Language Models (LLMs) are revolutionizing the field of computing
education with their powerful code-generating capabilities. Traditional
pedagogical practices have focused on code writing tasks, but there is now a
shift in importance towards code reading, comprehension and evaluation of
LLM-generated code. Alongside this shift, an important new skill is emerging --
the ability to solve programming tasks by constructing good prompts for
code-generating models. In this work we introduce a new type of programming
exercise to hone this nascent skill: 'Prompt Problems'. Prompt Problems are
designed to help students learn how to write effective prompts for AI code
generators. A student solves a Prompt Problem by crafting a natural language
prompt which, when provided as input to an LLM, outputs code that successfully
solves a specified programming task. We also present a new web-based tool
called Promptly which hosts a repository of Prompt Problems and supports the
automated evaluation of prompt-generated code. We deploy Promptly for the first
time in one CS1 and one CS2 course and describe our experiences, which include
student perceptions of this new type of activity and their interactions with
the tool. We find that students are enthusiastic about Prompt Problems, and
appreciate how the problems engage their computational thinking skills and
expose them to new programming constructs. We discuss ideas for the future
development of new variations of Prompt Problems, and the need to carefully
study their integration into classroom practice.Comment: Accepted to SIGCSE'24. arXiv admin note: substantial text overlap
with arXiv:2307.1636
Interactions with Prompt Problems: A New Way to Teach Programming with Large Language Models
Large Language Models (LLMs) have upended decades of pedagogy in computing
education. Students previously learned to code through \textit{writing} many
small problems with less emphasis on code reading and comprehension. Recent
research has shown that free code generation tools powered by LLMs can solve
introductory programming problems presented in natural language with ease. In
this paper, we propose a new way to teach programming with Prompt Problems.
Students receive a problem visually, indicating how input should be transformed
to output, and must translate that to a prompt for an LLM to decipher. The
problem is considered correct when the code that is generated by the student
prompt can pass all test cases. In this paper we present the design of this
tool, discuss student interactions with it as they learn, and provide insights
into this new class of programming problems as well as the design tools that
integrate LLMs.Comment: accepted for CHI 202
Characterizing the impact of urban emissions on regional aerosol particles: airborne measurements during the MEGAPOLI experiment
The MEGAPOLI (Megacities: Emissions, urban, regional and Global
Atmospheric POLlution and climate effects, and Integrated tools for
assessment and mitigation) experiment took place in July 2009. The aim of this campaign
was to study the aging and reactions of aerosol and gas-phase emissions in
the city of Paris. Three ground-based measurement sites and several mobile
platforms including instrument equipped vehicles and the ATR-42 aircraft
were involved. We present here the variations in particle- and gas-phase
species over the city of Paris, using a combination of high-time resolution
measurements aboard the ATR-42 aircraft. Particle chemical composition was
measured using a compact time-of-flight aerosol mass spectrometer (C-ToF-AMS), giving detailed information on the non-refractory submicron
aerosol species. The mass concentration of black carbon (BC), measured by a
particle absorption soot photometer (PSAP), was used as a marker to identify
the urban pollution plume boundaries. Aerosol mass concentrations and
composition were affected by air-mass history, with air masses that spent
longest time over land having highest fractions of organic aerosol and
higher total mass concentrations. The Paris plume is mainly composed of
organic aerosol (OA), BC, and nitrate aerosol, as well as high
concentrations of anthropogenic gas-phase species such as toluene, benzene,
and NO<sub>x</sub>. Using BC and CO as tracers for air-mass dilution, we observe
the ratio of ÎOA / ÎBC and ÎOA / ÎCO increase
with increasing photochemical age (âlog(NO<sub>x</sub> / NO<sub>y</sub>)). Plotting the
equivalent ratios of different organic aerosol species (LV-OOA, SV-OOA, and
HOA) illustrate that the increase in OA is a result of secondary organic
aerosol (SOA) formation. Within Paris the changes in the ÎOA / ΔCO are similar to those observed during other studies in London, Mexico
City, and in New England, USA. Using the measured SOA volatile organic compounds (VOCs) species together
with organic aerosol formation yields, we were able to predict ~50% of
the measured organics. These airborne measurements during the MEGAPOLI
experiment show that urban emissions contribute to the formation of OA and
have an impact on aerosol composition on a regional scale
Intracranial stimulation for children with epilepsy
OBJECTIVES: To evaluate the efficacy of intracranial stimulation to treat refractory epilepsy in children. METHODS: This is a retrospective analysis of a pilot study on all 8 children who had intracranial electrical stimulation for the investigation and treatment of refractory epilepsy at King's College Hospital between 2014 and 2015. Five children (one with temporal lobe epilepsy and four with frontal lobe epilepsy) had subacute cortical stimulation (SCS) for a period of 20-161Â h during intracranial video-telemetry. Efficacy of stimulation was evaluated by counting interictal discharges and seizures. Two children had thalamic deep brain stimulation (DBS) of the centromedian nucleus (one with idiopathic generalized epilepsy, one with presumed symptomatic generalized epilepsy), and one child on the anterior nucleus (right fronto-temporal epilepsy). The incidence of interictal discharges was evaluated visually and quantified automatically. RESULTS: Among the three children with DBS, two had >60% improvement in seizure frequency and severity and one had no improvement. Among the five children with SCS, four showed improvement in seizure frequency (>50%) and one chid did not show improvement. Procedures were well tolerated by children. CONCLUSION: Cortical and thalamic stimulation appear to be effective and well tolerated in children with refractory epilepsy. SCS can be used to identify the focus and predict the effects of resective surgery or chronic cortical stimulation. Further larger studies are necessary
CSF Rhinorrhea After Endonasal Intervention to the Skull Base (CRANIAL) â Part 2:Impact of COVID-19
Background During the pandemic, there has been a concern about the increased risk of perioperative mortality for patients with COVID-19, and the transmission risk to healthcare workers, particularly during endonasal neurosurgical operations. The Pituitary Society produced recommendations to guide management during this era. We sought to assess contemporary neurosurgical practice and the impact of COVID-19. Methods A multicentre, prospective, observational cohort study was conducted at twelve tertiary neurosurgical units (UK and Ireland). Data were collected from March 23rd-July 31st, 2020 inclusive. Data points collected were patient demographics, pre-operative COVID-19 testing, intra-operative operative modifications, and 30-day COVID infection rates. Results 124 patients were included. 116 patients (n=116/124, 94%) underwent COVID-19 testing pre-operatively (TSA: 97/105, 92%; EEA: 19/19, 100%). One patient (n=1/115, 1%) tested positively for COVID-19 pre-operatively, requiring a delay of operation until the infection was confirmed as resolved. Asides from transient diabetes insipidus; no other complications were reported for this case. All theatre staff wore at least level 2 PPE. Adaptations to surgical techniques included minimising drilling, draping modifications, and using nasal iodine wash. At 30 days postoperatively, there was no evidence of COVID infection (symptoms or on formal testing) in our cohort, and no mortality. Conclusions Preoperative screening protocols and operative modifications have facilitated endonasal neurosurgery during the COVID-19 pandemic, with Pituitary Society guidelines followed for the majority of these operations. There was no evidence of COVID infection in our cohort, and no mortality, supporting the use of risk mitigation strategies to continue endonasal neurosurgery in subsequent pandemic waves
CSF Rhinorrhoea After Endonasal Intervention to the Skull Base (CRANIAL) - Part 1: Multicenter Pilot Study
Background:
CRANIAL (CSF Rhinorrhoea After Endonasal Intervention to the Skull Base) is a prospective, multicentre observational study seeking to determine: (1) the scope of skull base repair methods used; and (2) corresponding rates of postoperative CSF rhinorrhoea in endonasal transsphenoidal (TSA) expanded endonasal approaches (EEA) for skull base tumours. We sought to pilot the project - assessing the feasibility and acceptability by gathering preliminary data. /
Methods:
A prospective, observational cohort pilot study was carried out at twelve tertiary UK neurosurgical units. Feedback regarding project positives and challenges were qualitatively analysed. /
Results:
187 cases were included, 159 TSA (85%) and 28 EEA (15%). The most common pathologies included: pituitary adenomas (n=141/187), craniopharyngiomas (n=13/187) and skull-base meningiomas (n=4/187). The most common skull base repair techniques used were tissue glues (n=132/187, most commonly TisseelÂź), grafts (n=94/187, most commonly fat autograft or Spongostanâą) and vascularised flaps (n=51/187, most commonly nasoseptal). These repairs were most frequently supported by nasal packs (n=125/187) and lumbar drains (n=22/187). Biochemically-confirmed CSF rhinorrhoea occurred in 6/159 (3.8%) TSA and 2/28 (7.1%) EEA. Four TSA (3%) and two EEA (7%) cases required operative management for CSF rhinorrhoea (CSF diversion or direct repair). Qualitative feedback was largely positive (themes included: user-friendly and efficient data collection, strong support from senior team members) demonstrating acceptability. /
Conclusions:
Our pilot experience highlights the acceptability and feasibility of CRANIAL. There is a precedent for multicentre dissemination of this project, in order to establish a benchmark of contemporary skull base neurosurgery practice, particularly with respect to EEA cases
CSF Rhinorrhoea After Endonasal Intervention to the Skull Base (CRANIAL) - Part 1:Multicenter Pilot Study
Background CRANIAL (CSF Rhinorrhoea After Endonasal Intervention to the Skull Base) is a prospective, multicentre observational study seeking to determine: (1) the scope of skull base repair methods used; and (2) corresponding rates of postoperative CSF rhinorrhoea in endonasal transsphenoidal (TSA) expanded endonasal approaches (EEA) for skull base tumours. We sought to pilot the project - assessing the feasibility and acceptability by gathering preliminary data. Methods A prospective, observational cohort pilot study was carried out at twelve tertiary UK neurosurgical units. Feedback regarding project positives and challenges were qualitatively analysed. Results 187 cases were included, 159 TSA (85%) and 28 EEA (15%). The most common pathologies included: pituitary adenomas (n=141/187), craniopharyngiomas (n=13/187) and skull-base meningiomas (n=4/187). The most common skull base repair techniques used were tissue glues (n=132/187, most commonly TisseelÂź), grafts (n=94/187, most commonly fat autograft or Spongostanâą) and vascularised flaps (n=51/187, most commonly nasoseptal). These repairs were most frequently supported by nasal packs (n=125/187) and lumbar drains (n=22/187). Biochemically-confirmed CSF rhinorrhoea occurred in 6/159 (3.8%) TSA and 2/28 (7.1%) EEA. Four TSA (3%) and two EEA (7%) cases required operative management for CSF rhinorrhoea (CSF diversion or direct repair). Qualitative feedback was largely positive (themes included: user-friendly and efficient data collection, strong support from senior team members) demonstrating acceptability. Conclusions Our pilot experience highlights the acceptability and feasibility of CRANIAL. There is a precedent for multicentre dissemination of this project, in order to establish a benchmark of contemporary skull base neurosurgery practice, particularly with respect to EEA cases. Keywords Cerebrospinal fluid rhinorrhoeaCSFCerebrospinal fluid leakskull base surgeryendoscopic endonasalEE
Altimetry for the future: Building on 25 years of progress
In 2018 we celebrated 25 years of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology. The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the âGreenâ Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instrumentsâ development and satellite missionsâ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion