Origins of the Stokes Shift in PbS Quantum Dots: Impact of Polydispersity, Ligands, and Defects

Liu, Yun,Kim, Donghun,Morris, Owen P.,Zhitomirsky, David,Grossman, Jeffrey C. American Chemical Society 2018 ACS NANO Vol.12 No.3

<P>Understanding the origins of the excessive Stokes shift in the lead chalcogenides family of colloidal quantum dots (CQDs) is of great importance at both the fundamental and applied levels; however, our current understanding is far from satisfactory. Here, utilizing a combination of <I>ab initio</I> computations and UV-vis and photoluminescence measurements, we investigated the contributions to the Stokes shift from polydispersity, ligands, and defects in PbS CQDs. The key results are as follows: (1) The size and energetic disorder of a polydisperse CQD film increase the Stokes shift by 20 to 50 meV compared to that of an isolated CQD; (2) Franck-Condon (FC) shifts increase as the electronegativities of the ligands increase, but the variations are small (<15 meV). (3) Unlike the aforementioned two minor factors, the presence of certain intrinsic defects such as V<SUB>Cl</SUB><SUP>+</SUP> (in Cl-passivated CQDs) can cause substantial electron density localization of the band edge states and consequent large FC shifts (100s of meV). This effect arising from defects can explain the excessive Stokes shifts in PbS CQDs and improve our understanding of the optical properties of PbS CQDs.</P> [FIG OMISSION]</BR>

Irregular frequency effects in the calculations of the drift forces

Liu, Yujie,Falzarano, Jeffrey M. Techno-Press 2019 Ocean systems engineering Vol.9 No.1

Accurate calculation of the mean drift forces and moments is necessary when studying the higher order excitations on the floater in waves. When taking the time average of the second order forces and moments, the second order potential and motion diminish with only the first order terms remained. However, in the results of the first order forces or motions, the irregular frequency effects are often observed in higher frequencies, which will affect the accuracy of the calculation of the second order forces and moments. Therefore, we need to pay close attention to the irregular frequency effects in the mean drift forces. This paper will discuss about the irregular frequency effects in the calculations of the mean drift forces and validate our in-house program MDL Multi DYN using some examples which are known to have irregular frequency effects. Finally, we prove that it is necessary to remove the effects and demonstrate that the effectiveness of the formula and methods adopted in the development of our program.

Control of Single-Molecule Junction Conductance of Porphyrins via a Transition-Metal Center

Liu, Zhen-Fei,Wei, Sujun,Yoon, Hongsik,Adak, Olgun,Ponce, Ingrid,Jiang, Yivan,Jang, Woo-Dong,Campos, Luis M.,Venkataraman, Latha,Neaton, Jeffrey B. American Chemical Society 2014 NANO LETTERS Vol.14 No.9

<P>Using scanning tunneling microscope break-junction experiments and a new first-principles approach to conductance calculations, we report and explain low-bias charge transport behavior of four types of metal–porphyrin–gold molecular junctions. A nonequilibrium Green’s function approach based on self-energy corrected density functional theory and optimally tuned range-separated hybrid functionals is developed and used to understand experimental trends quantitatively. Importantly, due to the localized d states of the porphyrin molecules, hybrid functionals are essential for explaining measurements; standard semilocal functionals yield qualitatively incorrect results. Comparing directly with experiments, we show that the conductance can change by nearly a factor of 2 when different metal cations are used, counter to trends expected from gas-phase ionization energies which are relatively unchanged with the metal center. Our work explains the sensitivity of the porphyrin conductance with the metal center via a detailed and quantitative portrait of the interface electronic structure and provides a new framework for understanding transport quantitatively in complex junctions involving molecules with localized d states of relevance to light harvesting and energy conversion.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2014/nalefd.2014.14.issue-9/nl5025062/production/images/medium/nl-2014-025062_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl5025062'>ACS Electronic Supporting Info</A></P>

Broad tuning of whispering-gallery modes in silicon microdisks

Shainline, Jeffrey M.,Fernandes, Gustavo,Liu, Zhijun,Xu, Jimmy The Optical Society 2010 Optics express Vol.18 No.14

<P>Silicon microdisks with dynamically-tunable resonance spectra are achieved with nanoscale, in-plane silicon electrical contacts in a single lithographic step. Electrical current is passed through the devices to enable thermal tuning via joule heating. A 14nm wavelength shift is demonstrated with 1.6mW power consumption in devices with >20nm free spectral ranges and quality factors exceeding 20,000. Spectral shifts equal to a full width at half maximum can be achieved with approximately 10microW tuning power for a mode with quality factor of 20,000.</P>

A more efficient numerical evaluation of the green function in finite water depth

Xie, Zhitian,Liu, Yujie,Falzarano, Jeffrey Techno-Press 2017 Ocean systems engineering Vol.7 No.4

The Gauss-Legendre integral method is applied to numerically evaluate the Green function and its derivatives in finite water depth. In this method, the singular point of the function in the traditional integral equation can be avoided. Moreover, based on the improved Gauss-Laguerre integral method proposed in the previous research, a new methodology is developed through the Gauss-Legendre integral. Using this new methodology, the Green function with the field and source points near the water surface can be obtained, which is less mentioned in the previous research. The accuracy and efficiency of this new method is investigated. The numerical results using a Gauss-Legendre integral method show good agreements with other numerical results of direct calculations and series form in the far field. Furthermore, the cases with the field and source points near the water surface are also considered. Considering the computational efficiency, the method using the Gauss-Legendre integral proposed in this paper could obtain the accurate numerical results of the Green function and its derivatives in finite water depth and can be adopted in the near field.

Liposomal Bupivacaine Associated with Cost Savings during Postoperative Pain Management in Fragility Intertrochanteric Hip Fractures

Nainisha Chintalapudi,Avinesh Agarwalla,Jeffrey Bortman,Joana Lu,Hrayr G. Basmajian,Nirav H. Amin,Joseph N. Liu 대한정형외과학회 2022 Clinics in Orthopedic Surgery Vol.14 No.2

Background: Intertrochanteric hip fractures are among the most common and most expensive diagnoses in the Medicare population. Liposomal bupivacaine is a novel preparation of a commonly used analgesic agent that, when used intraoperatively, decreases narcotic requirements and hospital length of stay and increases the likelihood of discharge to home. The purpose of this investigation was to determine whether there was an economic benefit to utilizing intraoperative liposomal bupivacaine in patients with fragility intertrochanteric hip fractures in comparison to a group of patients who did not receive liposomal bupivacaine. Methods: This is a retrospective observational study performed at two academic medical centers. Fifty-six patients with intertrochanteric hip fractures treated with cephalomedullary nail implant who received standard hip fracture pain management protocol were compared to a cohort of 46 patients with intertrochanteric hip fractures who received additional intraoperative injections of liposomal bupivacaine. All other standards of care were identical. A cost analysis was completed including the cost of liposomal bupivacaine, operating room costs, and discharge destination. Statistical significance was set at p < 0.05. Results: Although the length of hospital stay was similar between the two groups (3.2 days vs. 3.8 days, p = 0.08), patients receiving intraoperative liposomal bupivacaine had a lower likelihood of discharge to a skilled nursing facility (84.8% vs. 96.4%, p = 0.002) and a longer operative time (73.4 minutes vs 67.2 minutes, p = 0.004). The cost-benefit analysis indicated that for an investment of $334.18 in the administration of 266 mg of liposomal bupivacaine, there was a relative saving of $1,323.21 compared to the control group. The benefit-cost ratio was 3.95, indicating a $3.95 benefit for each $1 spent in liposomal bupivacaine. Conclusions: Despite the increased initial cost, intraoperative use of liposomal bupivacaine was found to be a cost-effective intervention due to the higher likelihood of discharge to home during the postoperative management of patients with intertrochanteric hip fractures.

Effect of Diclazuril on the Bursa of Fabricius Morphology and SIgA Expression in Chickens Infected with Eimeria tenella

Bian-hua Zhou,Li-li Liu,Jeffrey Liu,Fu-wei Yuan,Er-jie Tian,Hong-wei Wang 대한기생충학열대의학회 2015 The Korean Journal of Parasitology Vol.53 No.6

Treatment of In-Stent Stenosis Following Flow Diversion of Intracranial Aneurysms with Cilostazol and Clopidogrel

Ehsan Dowlati,Kory B. Dylan Pasko,Jiaqi Liu,Charles A. Miller,Daniel R. Felbaum,Samir Sur,Jason J. Chang,Ai-Hsi Liu,Rocco A. Armonda,Jeffrey C. Mai 대한신경중재치료의학회 2021 Neurointervention Vol.16 No.3

In-stent stenosis is a feared complication of flow diversion treatment for cerebral aneurysms. We present 2 cases of patients treated with pipeline flow diversion for unruptured cerebral aneurysms. Initial perioperative dual antiplatelet therapy (DAPT) consisted of standard aspirin plus clopidogrel. At 6-month follow-up cerebral angiography, the patients were noted to have developed significant in-stent stenosis (63% and 53%). The patients were treated with cilostazol and clopidogrel for at least 6 months. Subsequent angiography at 1-year post-treatment showed significant improvement of the in-stent stenosis from 63% to 34% and 53% to 21%. The role of cilostazol as treatment of intracranial in-stent stenosis has not been previously described. Cilostazol’s vasodilatory effect and suppression of vascular smooth muscle proliferation provides ideal benefits in this setting. Cilostazol plus clopidogrel may be a safe and effective alternative to standard DAPT for treatment of in-stent stenosis following flow diversion and warrants further consideration and investigation.

Synthesis of Biocompatible PEG-Based Star Polymers with Cationic and Degradable Core for siRNA Delivery

Cho, Hong Y.,Srinivasan, Abiraman,Hong, Joanna,Hsu, Eric,Liu, Shiguang,Shrivats, Arun,Kwak, Dan,Bohaty, Andrew K.,Paik, Hyun-jong,Hollinger, Jeffrey O.,Matyjaszewski, Krzysztof American Chemical Society 2011 Biomacromolecules Vol.12 No.10

<P>Star polymers with poly(ethylene glycol) (PEG) arms and a degradable cationic core were synthesized by the atom transfer radical copolymerization (ATRP) of poly(ethylene glycol) methyl ether methacrylate macromonomer (PEGMA), 2-(dimethylamino)ethyl methacrylate (DMAEMA), and a disulfide dimethacrylate (cross-linker, SS) via an “<I>arm-first</I>” approach. The star polymers had a diameter ∼15 nm and were degraded under redox conditions by glutathione treatment into individual polymeric chains due to cleavage of the disulfide cross-linker, as confirmed by dynamic light scattering. The star polymers were cultured with mouse calvarial preosteoblast-like cells, embryonic day 1, subclone 4 (MC3T3-E1.4) to determine biocompatibility. Data suggest star polymers were biocompatible, with ≥80% cell viability after 48 h of incubation even at high concentration (800 μg/mL). Zeta potential values varied with N/P ratio confirming complexation with siRNA. Successful cellular uptake of the star polymers in MC3T3-E1.4 cells was observed by confocal microscopy and flow cytometry after 24 h of incubation.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/bomaf6/2011/bomaf6.2011.12.issue-10/bm2006455/production/images/medium/bm-2011-006455_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/bm2006455'>ACS Electronic Supporting Info</A></P>

Platinum-based nanocages with subnanometer-thick walls and well-defined, controllable facets

Zhang, Lei,Roling, Luke T.,Wang, Xue,Vara, Madeline,Chi, Miaofang,Liu, Jingyue,Choi, Sang-Il,Park, Jinho,Herron, Jeffrey A.,Xie, Zhaoxiong,Mavrikakis, Manos,Xia, Younan American Association for the Advancement of Scienc 2015 Science Vol.349 No.6246

<P><B>Etching platinum nanocage catalysts</B></P><P>Although platinum is an excellent catalyst for the oxygen reduction reaction that occurs in fuel cells, its scarcity continues to drive efforts to improve its utilization. Zhang <I>et al.</I> made nanocages of platinum by coating palladium nanocrystals with only a few layers of platinum and then etching away the palladium core (see the Perspective by Strasser). Platinum nanocages made using nanoscale octahedra and cubes of palladium displayed different catalytic activity for the oxygen reduction reaction.</P><P><I>Science</I>, this issue p. 412; see also p. 379</P><P>A cost-effective catalyst should have a high dispersion of the active atoms, together with a controllable surface structure for the optimization of activity, selectivity, or both. We fabricated nanocages by depositing a few atomic layers of platinum (Pt) as conformal shells on palladium (Pd) nanocrystals with well-defined facets and then etching away the Pd templates. Density functional theory calculations suggest that the etching is initiated via a mechanism that involves the formation of vacancies through the removal of Pd atoms incorporated into the outermost layer during the deposition of Pt. With the use of Pd nanoscale cubes and octahedra as templates, we obtained Pt cubic and octahedral nanocages enclosed by {100} and {111} facets, respectively, which exhibited distinctive catalytic activities toward oxygen reduction.</P>