Yiannis Kamarianakis | IBM Research (original) (raw)

Papers by Yiannis Kamarianakis

Pediatric Transplantation, Sep 24, 2018

Background: Listed pediatric heart transplant patients have the highest solid-organ waitlist mort... more Background: Listed pediatric heart transplant patients have the highest solid-organ waitlist mortality rate. The donor-recipient body weight (DRBW) ratio is the clinical standard for allograft size matching but may unnecessarily limit a patient's donor pool. To overcome DRBW ratio limitations, two methods of performing virtual heart transplant fit assessments were developed that account for patient-specific nuances. Method 1 uses an allograft total cardiac volume (TCV) prediction model informed by patient data wherein a matched allograft 3-D reconstruction is selected from a virtual library for assessment. Method 2 uses donor images for a direct virtual transplant assessment. Methods: Assessments were performed in medical image reconstruction software. The allograft model was developed using allometric/isometric scaling assumptions and cross-validation. Results: The final predictive model included gender, height, and weight. The 25th-, 50th-, and 75th-percentiles for TCV percentage errors were −13% (over-prediction), −1%, and 8% (under-prediction), respectively. Two examples illustrating the potential of virtual assessments are presented. Conclusion: Transplant centers can apply these methods to perform their virtual assessments using existing technology. These techniques have potential to improve organ allocation. With additional experience and refinement, virtual transplants may become standard of care for determining suitability of donor organ size for an identified recipient.

Remote Sensing of Environment, 2016

Journal of Applied Statistics, Oct 1, 2012

Frontiers of Earth Science, Dec 5, 2017

The impacts of land-cover composition on urban temperatures, including temperature extremes, are ... more The impacts of land-cover composition on urban temperatures, including temperature extremes, are well documented. Much less attention has been devoted to the consequences of land-cover configuration, most of which addresses land surface temperatures. This study explores the role of both composition and configuration-or land system architecture-of residential neighborhoods in the Phoenix metropolitan area, on near-surface air temperature. It addresses two-dimensional, spatial attributes of buildings, impervious surfaces, bare soil/ rock, vegetation and the "urbanscape" at large, from 50 m to 550 m at 100 m increments, for a representative 30-day high sun period. Linear mixed-effects models evaluate the significance of land system architecture metrics at different spatial aggregation levels. The results indicate that, controlling for land-cover composition and geographical variables, land-cover configuration, specifically the fractal dimension of buildings, is significantly associated with near-surface temperatures. In addition, statistically significant predictors related to composition and configuration appear to depend on the adopted level of spatial aggregation.

Photogrammetric Engineering and Remote Sensing, Feb 1, 2011

The ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) Global Digital Elevati... more The ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) Global Digital Elevation Model (GDEM), which was released in June 2009, provides elevation data for over 99 percent of Earth's land area. GDEM was found to contain significant anomalies mainly caused by residual clouds in the ASTER scenes, or by the algorithm used to generate the final GDEM from the variable number of individual DEMs. In this paper, the GDEM, for the whole area of Greece was validated by comparing it with reference DEMs with higher resolution derived either from aerial stereo imagery, or from ASTER raw data analysis; as well as with elevation values provided by a number of Geodetic Control Points (GCP) and GPS measurements. The vertical accuracy (at 95 percent confidence) was calculated to be more than 30 m (RMSE ϭ 16.01 m) when compared to the GCPs, whereas the vertical accuracy was calculated around 20 m (RMSE ϭ 11.08 m) when compared with the GPS derived elevations. It can be therefore stated that the current version of ASTER GDEM overall does not meet its pre-production estimated vertical accuracy of 20 m at 95 percent confidence over Greece, however, it can be used in several applications, such as topographic analysis, hydrological and geomorphological modeling, landscape visualization, and energy balance studies.

Abstract In this study, Advanced Very High Resolution Radiometer (AVHRR) thermal infrared records... more Abstract In this study, Advanced Very High Resolution Radiometer (AVHRR) thermal infrared records were used to estimate the spatial distribution of precipitable water (PW) over the broader area of Greece. PW was derived as a function of AVHRR thermal channels brightness temperature difference (ΔT). The PW–ΔT relationship was calibrated using the Moderate Resolution Imaging Spectroradiometer (MODIS) atmospheric product. Both MODIS derived PW and AVHRR derived ΔΤ were spatially aggregated in a grid of 5 x 5 ...

Computers & Geosciences, Mar 1, 2005

Die Dokumente auf EconStor dürfen zu eigenen wissenschaftlichen Zwecken und zum Privatgebrauch ge... more Die Dokumente auf EconStor dürfen zu eigenen wissenschaftlichen Zwecken und zum Privatgebrauch gespeichert und kopiert werden. Sie dürfen die Dokumente nicht für öffentliche oder kommerzielle Zwecke vervielfältigen, öffentlich ausstellen, öffentlich zugänglich machen, vertreiben oder anderweitig nutzen. Sofern die Verfasser die Dokumente unter Open-Content-Lizenzen (insbesondere CC-Lizenzen) zur Verfügung gestellt haben sollten, gelten abweichend von diesen Nutzungsbedingungen die in der dort genannten Lizenz gewährten Nutzungsrechte. Terms of use: Documents in EconStor may be saved and copied for your personal and scholarly purposes. You are not to copy documents for public or commercial purposes, to exhibit the documents publicly, to make them publicly available on the internet, or to distribute or otherwise use the documents in public. If the documents have been made available under an Open Content Licence (especially Creative Commons Licences), you may exercise further usage rights as specified in the indicated licence.

Journal of Applied Statistics, Aug 4, 2020

Traffic management authorities in metropolitan areas use real-time systems that analyze high-freq... more Traffic management authorities in metropolitan areas use real-time systems that analyze high-frequency measurements from fixed sensors, to perform short-term forecasting and incident detection for various locations of a road network. Published research over the last 20 years focused primarily on modeling and forecasting of traffic volumes and speeds. Traffic occupancy approximates vehicular density through the percentage of time a sensor detects a vehicle within a pre-specified time interval. It exhibits weekly periodic patterns and heteroskedasticity and has been used as a metric for characterizing traffic regimes (e.g. free flow, congestion). This article presents a Bayesian three-step model building procedure for parsimonious estimation of Threshold-Autoregressive (TAR) models, designed for location- day- and horizon-specific forecasting of traffic occupancy. In the first step, multiple regime TAR models reformulated as high-dimensional linear regressions are estimated using Bayesian horseshoe priors. Next, significant regimes are identified through a forward selection algorithm based on Kullback-Leibler (KL) distances between the posterior predictive distribution of the full reference model and TAR models with fewer regimes. Given the regimes, the forward selection algorithm can be implemented again to select significant autoregressive terms. In addition to forecasting, the proposed specification and model-building scheme, may assist in determining location-specific congestion thresholds and associations between traffic dynamics observed in different regions of a network. Empirical results applied to data from a traffic forecasting competition, illustrate the efficacy of the proposed procedures in obtaining interpretable models and in producing satisfactory point and density forecasts at multiple horizons.

Global Change Biology, Jan 12, 2022

Spatio-temporal patterns of throughfall (TF) have often been studied under forest canopies. Few r... more Spatio-temporal patterns of throughfall (TF) have often been studied under forest canopies. Few reports, however, have been made on small-scale TF variability in deciduous forest stands. In the present research, the spatial heterogeneity and temporal stability of TF under five individual persian oak trees (Quercus brantii var. Persica) was quantified. The research site was in the Zagros forests in western Iran, where mean annual precipitation and temperature are equal to 587.2 mm and 16.9 C, respectively. Data from 23 rainfall events were aggregated to assess the spatial correlation of TF. Variograms for TF beneath two of the five trees reached a stable sill at the range of 5-6 m. The redistribution of TF within the canopy was highly variable in time, attributable to seasonal variation in canopy foliation and meteorological factors. As the length of the sampling period increased, the spatial variability of TF decreased and the temporal stability of the TF pattern increased. Time stability plots of TF normalized with respect to mean and variance showed a moderate general persistence for all individual trees. We conclude that single trees modify the spatial distribution of TF reaching the forest floors.

Symmetry, Mar 2, 2023

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Bioengineering

During the vascular surgical reconstruction of aorto-iliac occlusive/aneurysmal disease, bifurcat... more During the vascular surgical reconstruction of aorto-iliac occlusive/aneurysmal disease, bifurcated grafts are used where vascular surgeons intra-operatively select the size and the relative lengths of the parent and daughter portions of the graft. Currently, clinical practice regarding the selection of the most favorable geometric configuration of the graft is an understudied research subject: decisions are solely based on the clinical experience of the operating surgeon. This manuscript aims to evaluate the hemodynamic performance of various diameters, D, of bifurcated aortic grafts and relate those with proximal/distal part length ratios (the angle φ between the limbs is used as a surrogate marker of the main body-to-limb length ratio) in order to provide insights regarding the effects of different geometries on the hemodynamic environment. To this end, a computationally intensive set of simulations is conducted, and the resulting data are analyzed with modern statistical regress...

Journal of Environmental Management

ETK-NTTS Proceedings New Techniques and Technologies for Statistics, 2001

Abstract: The aim of this paper is to model the Gross Regional Product of Greece at the prefectur... more Abstract: The aim of this paper is to model the Gross Regional Product of Greece at the prefecture/regional level accounting for the spatiotemporal evolution of each sector, as well as, the interdependencies of the three sectors used. Hierarchical multivariate Bayesian space-time models are used to achieve more flexible methods for the analysis of data concerning the national economy. The first stage of the hierarchical model specifies a measurement error process for the data at hand, in terms of a 'state'process. The second ...

Landscape and Urban Planning, 2017

The relationship between the characteristics of the urban land system and land surface temperatur... more The relationship between the characteristics of the urban land system and land surface temperature (LST) has received increasing attention in urban heat island and sustainability research, especially for desert cities. This research generally employs medium or coarser spatial resolution data and primarily focuses on the effects of a few classes of land-cover composition and pattern at the neighborhood or larger level using regression models. This study explores the effects of land system architecture-composition and configuration, both pattern and shape, of fine-grain land-cover classes-on LST of single family residential parcels in the Phoenix, Arizona (southwestern USA) metropolitan area. A 1 m resolution land-cover map is used to calculate land architecture metrics at the parcel level, and 6.8 m resolution MODIS/ASTER data are employed to retrieve LST. Linear mixed-effects models quantify the impacts of land configuration on LST at the parcel scale, controlling for the effects of land composition and neighborhood characteristics. Results indicate that parcel-level land-cover composition has the strongest association with daytime and nighttime LST, but the configuration of this cover, foremost compactness and concentration, also affects LST, with different associations between land architecture and LST at nighttime and daytime. Given information on land system architecture at the parcel level, additional information based on geographic and socioeconomic variables does not improve the generalization capability of the statistical models. The results point the way towards parcel-level land-cover design that helps to mitigate the urban heat island

Theoretical and Applied Climatology, 2020

Air temperatures in urban environments are usually obtained from sparse weather stations that pro... more Air temperatures in urban environments are usually obtained from sparse weather stations that provide limited information with regard to spatial patterns. Effective methods that predict air temperatures (T air) in urban areas are based on statistical models which utilize remotely sensed and geographic data. This work aims to compute T air predictions for diurnal and nocturnal time intervals using predictive models that do not exploit information on Land Surface Temperatures. The models are developed based on explanatory variables that describe the urban morphology, land cover and terrain, aggregated at 100 m × 100 m resolution, combined with in situ T air measurements from urban meteorological stations. The case study is the urban and per-urban area of Heraklion, Greece, where a dense meteorological station network is available since 2016. Moran's eigenvector filtering and an autoregressive moving average residual specification are implemented to account for spatial and temporal correlations. The statistical models display satisfactory predictive performance, with mean annual Mean Absolute Error (MAE) equal to 0.36°C, 0.34°C, 0.42°C and 0.54°C,

KSCE Journal of Civil Engineering, 2020

The use of alternative project delivery methods has grown significantly over the last two decades... more The use of alternative project delivery methods has grown significantly over the last two decades. One such method is design-build (DB), which has been increasingly used due to its improved project cost and schedule performance. However, the project itself is only a fraction of the lifecycle of a built facility. Therefore, there is a need to understand whether delivery methods also impact the long-term performance of facilities. This paper focuses on quantifying the long-term performance impact of DB on pavements, compared to pavements delivered using the traditional design-bid-build (DBB) method. The international roughness index is selected as the metric to compare ride quality across projects. In total, the authors collected 9,946 data points representing 37 unique lane directions from 26 projects in six states, which they analyzed using linear mixed-effects methods. Results show that long-term performance of asphalt concrete pavement resurfacing DB projects is superior to that of comparable DBB projects by an equivalent of eight years of pavement life. A life cycle cost analysis shows the estimated monetary impact of these findings on the National Highway System is around $100 billion over the next 45 years. Design-build International roughness index Long-term performance Linear mixed-effects Asphalt pavement Portland cement concrete pavement CORRESPONDENCE Namho Cho

The Journal of Heart and Lung Transplantation, 2018

improve musculoskeletal conditioning and exercise efficiency during the pre-transplant period, wh... more improve musculoskeletal conditioning and exercise efficiency during the pre-transplant period, which may impact post-transplant outcomes.

Pediatric Transplantation, Sep 24, 2018

Remote Sensing of Environment, 2016

Journal of Applied Statistics, Oct 1, 2012

Frontiers of Earth Science, Dec 5, 2017

Photogrammetric Engineering and Remote Sensing, Feb 1, 2011

Computers & Geosciences, Mar 1, 2005

Journal of Applied Statistics, Aug 4, 2020

Global Change Biology, Jan 12, 2022

Symmetry, Mar 2, 2023

Bioengineering

Journal of Environmental Management

ETK-NTTS Proceedings New Techniques and Technologies for Statistics, 2001

Landscape and Urban Planning, 2017

Theoretical and Applied Climatology, 2020

KSCE Journal of Civil Engineering, 2020

The Journal of Heart and Lung Transplantation, 2018

Joint Statistical Meeting Proceedings, 2732-2738, 2014

This article presents a parametric time-series model for short-term traffic forecasting, which ac... more This article presents a parametric time-series model for short-term traffic forecasting, which accounts for space-time dependencies and cross-correlations of traffic variables. In the adopted framework, a separate model is built for each measurement location in the network. Each model may contain some hundreds of potentially useful predictors, that contain information from other locations in the network; the influential ones are chosen via a 2-step, penalized estimation scheme, namely, adaptive LASSO. In the Athens data, the method achieves approximately 90% 1-step forecast accuracy on 3-minute volumes, which declines slowly as the forecast-horizon increases; the observed forecasting performance for occupancies is not as satisfactory though. An advantage of the proposed approach is that it is readily able to be automated.