Dr. Timothy  Lee   image

Dr. Timothy Lee

2500 Pocoshock Pl Suite 104
North Chesterfield VA 23235
804 769-9305
Medical School: Other - Unknown
Accepts Medicare: No
Participates In eRX: No
Participates In PQRS: No
Participates In EHR: No
License #: 0116025953
NPI: 1568800019
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Phase matched parametric amplification via four-wave mixing in optical microfibers. - Optics letters
Four-wave mixing (FWM) based parametric amplification in optical microfibers (OMFs) is demonstrated over a wavelength range of over 1000 nm by exploiting their tailorable dispersion characteristics to achieve phase matching. Simulations indicate that for any set of wavelengths satisfying the FWM energy conservation condition there are two diameters at which phase matching in the fundamental mode can occur. Experiments with a high-power pulsed source working in conjunction with a periodically poled silica fiber (PPSF), producing both fundamental and second harmonic signals, are undertaken to investigate the possibility of FWM parametric amplification in OMFs. Large increases of idler output power at the third harmonic wavelength were recorded for diameters close to the two phase matching diameters. A total amplification of more than 25 dB from the initial signal was observed in a 6 mm long optical microfiber, after accounting for the thermal drift of the PPSF and other losses in the system.
Characterization of the Azirinyl Cation and Its Isomers. - The journal of physical chemistry. A
The azirinyl cation (C2H2N(+)) and its geometrical isomers could be present in the interstellar medium. The C2H2N(+) isomers are, however, difficult to identify in interstellar chemistry because of the lack of high-resolution spectroscopic data from laboratory experiments. Ab initio quantum chemical methods were used to characterize the structures, relative energies, and spectroscopic and physical properties of the low energy isomers of the azirinyl cation. We have employed second-order Møller-Plesset perturbation theory (MP2), second-order Z-averaged perturbation theory (ZAPT2), and coupled cluster theory with singles and doubles with perturbative triples CCSD(T) methods along with large correlation consistent basis sets such as cc-pVTZ, cc-pCVTZ, cc-pVQZ, cc-pCVQZ, and cc-pV5Z. Harmonic vibrational frequencies, dipole moments, rotational constants, and proton affinities for the lowest energy isomers were calculated using the CCSD(T) method. Azirinyl cation, a cyclic isomer, is lowest in energy at all levels of theory employed. Azirinyl cation is followed by the cyanomethyl cation (H2CCN)(+), isocyanomethyl cation (H2CNC)(+), and a quasilinear HCCNH(+) cation, which are 13.8, 17.3, and 21.5 kcal mol(-1) above the cyclic isomer, respectively, at the CCSD(T)/cc-pV5Z level of theory. The lowest three isomers all have C2v symmetry and (1)A1 ground electronic states. The quasilinear HCCNH(+) cation has a Cs symmetry planar structure, and a (3)A″ electronic ground state, unlike what some previous work suggested.
Fatal Falls in New York City: An Autopsy Analysis of Injury Patterns. - The American journal of forensic medicine and pathology
Falls from heights are an important cause of unintentional fatal injury. We investigated the relationship between the characteristics of fatal falls and resulting injury patterns.We reviewed prospectively collected data from the Office of Chief Medical Examiner in New York City between 2000 and 2010. Data included fall height, work or non-work related, use of safety equipment, intentionality, specific organ injuries, and death on impact. The primary outcome was organ injury based on fall height.Higher falls were associated with hemorrhage as well as rib and various organ injuries. Organ injury pattern did not differ based on work status. The presence of equipment misuse or malfunction was associated with more deaths upon impact. Victims of falls from 200 ft or higher were 11.59 times more likely to die on impact than from lower than 25 ft.Fall height and work-related falls were significantly associated with death on impact. This is a public health issue, as 13% of falls were work related and 4% of falls were due to improper use of safety equipment. Some work-related falls are potentially preventable with proper safety equipment use. Understanding patterns of injury may play a role in prevention and management of survivors in the acute period.
Assessment of quality of life outcomes using the pediatric quality of life inventory survey in prenatally diagnosed congenital diaphragmatic hernia patients. - Journal of pediatric surgery
Congenital diaphragmatic hernia patients can have significant postnatal morbidity. To date, there has been no quality of life (QOL) study in a prenatally diagnosed CDH patient population, assessing prenatal disease severity and QOL. The purpose of this pilot study was to assess the QOL in a single institution fetal center CDH experience.The study was a retrospective cohort study of CDH patients diagnosed by fetal ultrasound and MRI at a fetal center between March 2002-March 2014. Parents of children ≥2years were contacted by telephone to participate in the validated Pediatric Quality of Life Inventory (PedsQL™, Version 4.0).Of 95 CDH survivors, 68 met inclusion criteria, of which 28 (42%) completed the survey (mean age, range: 5.5, 2.3-11.7years). Based on prenatal markers of disease severity, there were no differences in performance between those with mild or severe forms of CDH. Overall, patients had minimal QOL limitations, but those with limitations had a higher risk for oxygen dependence at 30days of life (71%v. 29%, OR 0.16, CI, 0.031-0.82, p=0.02). ECMO was not associated with significantly worse QOL in physical or psychosocial functioning. Cronbach's alpha reliability coefficient yielded a correlation of 0.951 for the overall survey, 0.911 for physical functioning, and 0.901 for psychosocial functioning questions.Patients that are prenatally diagnosed with severe forms of CDH have similar QOL outcomes across all categories of physical and psychosocial functioning. This pilot study is encouraging and may allow improved counseling for expectant parents of CDH patients.Copyright © 2015. Published by Elsevier Inc.
The anharmonic quartic force field infrared spectra of three polycyclic aromatic hydrocarbons: Naphthalene, anthracene, and tetracene. - The Journal of chemical physics
Current efforts to characterize and study interstellar polycyclic aromatic hydrocarbons (PAHs) rely heavily on theoretically predicted infrared (IR) spectra. Generally, such studies use the scaled harmonic frequencies for band positions and double harmonic approximation for intensities of species, and then compare these calculated spectra with experimental spectra obtained under matrix isolation conditions. High-resolution gas-phase experimental spectroscopic studies have recently revealed that the double harmonic approximation is not sufficient for reliable spectra prediction. In this paper, we present the anharmonic theoretical spectra of three PAHs: naphthalene, anthracene, and tetracene, computed with a locally modified version of the SPECTRO program using Cartesian derivatives transformed from Gaussian 09 normal coordinate force constants. Proper treatments of Fermi resonances lead to an impressive improvement on the agreement between the observed and theoretical spectra, especially in the C-H stretching region. All major IR absorption features in the full-scale matrix-isolated spectra, the high-temperature gas-phase spectra, and the most recent high-resolution gas-phase spectra obtained under supersonically cooled molecular beam conditions in the CH-stretching region are assigned.
Electronically Excited States of Anisotropically Extended Singly-Deprotonated PAH Anions. - The journal of physical chemistry. A
Polycyclic aromatic hydrocarbons (PAHs) play a significant role in the chemistry of the interstellar medium (ISM) as well as in hydrocarbon combustion. These molecules can have high levels of diversity with the inclusion of heteroatoms and the addition or removal of hydrogens to form charged or radical species. There is an abundance of data on the cationic forms of these molecules, but there have been many fewer studies on the anionic species. The present study focuses on the anionic forms of deprotonated PAHs. It has been shown in previous work that PAHs containing nitrogen heteroatoms (PANHs) have the ability to form valence excited states giving anions electronic absorption features. This work analyzes how the isoelectronic pure PAHs behave under similar structural constructions. Singly deprotonated forms of benzene, naphthalene, anthracene, and tetracene classes are examined. None of the neutral-radicals possess dipole moments large enough to support dipole-bound excited states in their corresponding closed-shell anions. Even though the PANH anion derivatives support valence excited states for three-ringed structures, it is not until four-ringed structures of the pure PAH anion derivatives that valence excited states are exhibited. However, anisotropically extended PAHs larger than tetracene will likely exhibit valence excited states. The relative energies for the anion isomers are very small for all of the systems in this study.
Impact of the surgeon of the week system in an academic pediatric surgery practice. - Journal of pediatric surgery
A pilot rounding surgeon of the week (SOW) program was implemented in our institution on July 2013 to improve patient care through focused attending rounds. The purpose of this study was to assess the impact of the SOW.We performed a descriptive retrospective study from a single, large-volume academic center. Data were collected from July to December 2013 (post-SOW) and compared to July to December 2012 (pre-SOW). Outcomes included patient safety (safety reports) and team productivity (billing data). We also evaluated nursing satisfaction through a 10-point Likert scale survey.The total number of patient safety complaints decreased after the SOW (37 pre-SOW versus 27 post-SOW). Work relative value units (wRVUs) increased by 8% while nonoperative billing increased by 15%. Twenty of the daytime nursing staff completed the survey and overall satisfaction with the SOW was 8.3. Twelve were employed prior to the SOW and, when analyzed independently, the proportion of employees satisfied with nursing to physician communication was higher after the SOW (55% pre-SOW vs. 83% post-SOW, p=0.13) as was perception of parental satisfaction (33% vs. 75%, p=0.04).The SOW program appears to improve patient safety as evidenced by a decrease in patient safety events. Additionally, the SOW program led to higher ancillary staffing satisfaction and perceived parental satisfaction without decreasing revenue. This study suggests that the SOW may be a beneficial program that could be considered at other large-volume institutions.Copyright © 2015 Elsevier Inc. All rights reserved.
A novel multimodal computational system using near-infrared spectroscopy to monitor cerebral oxygenation during assisted ventilation in CDH patients. - Journal of pediatric surgery
The aim of this study was to create a computational simulator to serve as an early alert system for cerebral hypoxemia prior to the onset of clinical symptoms.Neonates with congenital diaphragmatic hernia (Jan 2010-Dec 2014) were recruited to collect continuous measurements of cerebral tissue oxygen saturation (cStO2) using a near-infrared spectroscopy (NIRS) device (FORE-SIGHT®, CASMED). Clinicians were blinded to NIRS data and treated infants based on pre-established clinical protocols. Charts were reviewed retrospectively to identify clinical events of hypoxemia (spontaneous, sustained decrease in preductal SpO2<85% leading to ventilator changes). We developed a computational algorithm that determined baseline values, variability and event data for each patient.Twenty-three of 36 patients enrolled met data criteria. The algorithm anticipated an event at least 15minutes prior to the event in 77% of cases, with an average pre-event detection of 47minutes (range 16-122minutes). Post-event StO2 (SpO2<85%) was determined to be 63.7%±11.7. In this computational model, the sensitivity to distinguish low states of cerebral perfusion was 94% with a specificity of 96%.We have developed a computational algorithm with an early warning system that has the potential of being translated into a real-time clinical interface that may improve management of neonates.Copyright © 2016 Elsevier Inc. All rights reserved.
Risk-stratification of severity for infants with CDH: Prenatal versus postnatal predictors of outcome. - Journal of pediatric surgery
The purpose of this study was to compare the predication accuracy of a newly described postnatally-based clinical prediction model to fetal imaging-based predictors of mortality for infants with CDH.We performed a retrospective review of all CDH patients treated at a comprehensive fetal care center from January 2004 to January 2014. Prenatal data reviewed included lung-to-head ratio (LHR), observed/expected-total fetal lung volume (O/E-TFLV), and percent liver herniation (%LH). Based on the postnatal prediction model, neonates were categorized as low, intermediate, and high risk of death. The primary outcome was 6-month mortality.Of 176 CDH patients, 58 had a major cardiac anomaly, and 28 had a genetic anomaly. Patients with O/E-TFLV <35% and %LH >20% were at increased risk for mortality (44% and 36%, respectively). There was a significant difference in mortality between low, intermediate, and high-risk groups (4% vs. 22% vs. 51%; p<0.001). On multivariate regression, the O/E-TFLV and postnatal-based mortality risk score were the two independent predictors of 6-month mortality.The CDH Study Group postnatal predictive model provides good discrimination among three risk groups in our patient cohort. The prenatal MRI-based O/E-TFLV is the strongest prenatal predictor of 6-month mortality in infants with CDH and will help guide prenatal counseling and discussions regarding fetal intervention and perinatal management.Copyright © 2016 Elsevier Inc. All rights reserved.
High-volume hydrodissection for abdominally based free flaps: Preliminary results. - Microsurgery
A novel method of high-volume hydrodissection that provides both subfascial and intramuscular perforator dissection of deep inferior epigastric perforators has been safely demonstrated in animals. This manuscript demonstrates our preliminary results when translating this technique to humans.A retrospective review was performed of all free-flap breast reconstructions utilizing the high-volume hydrodissection technique performed by the senior author (DS) at the University of Florida Medical Center from January 2014 to June 2015.Twenty-one patients underwent 31 free-flap breast reconstructions during the study period utilizing the high-volume hydrodissection technique. No patients were lost to follow-up which averaged 8.2 months. Complications included 1 partial flap necrosis (<10%), 1 breast hematoma, 1 abdominal bulge, 2 flaps with minimal fat necrosis (<5%), and 1 abdominal wall cellulitis.High-volume hydrodissection is a safe technique to facilitate dissection of abdominally based free flaps for breast reconstruction. © 2015 Wiley Periodicals, Inc. Microsurgery, 2015.© 2015 Wiley Periodicals, Inc.

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