Prepandemic Social Integration: Protection or Risk for Older Adults in the Time of COVID-19?

OBJECTIVES: To examine the association between prepandemic social integration and posttraumatic stress disorder (PTSD) symptoms during the coronavirus disease 2019 (COVID-19) pandemic and test whether the association is mediated by social support received and social events missed during the pandemic. We also explored age, race, gender, and socioeconomic differences in the association. METHODS: We adopted a prospective design. Path analysis was conducted using data from the COVID-19 supplement (2020) and the 2019 wave of the National Health and Aging Trends Study (NHATS). The sample represents Medicare beneficiaries aged 70 years and older (N = 2,694). Social integration was measured using a six-item index. A standardized scale assessed PTSD symptoms. Both social support received and social events missed were single-item measures. The analysis controlled for sociodemographic characteristics, prepandemic physical and mental health, and coronavirus exposure during the pandemic. RESULTS: Prepandemic social integration was positively associated with PTSD symptoms during the pandemic. The association was primarily mediated by social events missed-high levels of prepandemic social integration were associated with missing more social events during the pandemic resulting in more PTSD symptoms. Social support received was also a mediator-social integration was positively associated with social support received during the pandemic, with more received support associated with greater PTSD symptoms. Prepandemic social integration had no significant direct effect on PTSD symptoms. The direct, indirect, and total effects of social integration on PTSD symptoms did not significantly differ by age, race, gender, education, or poverty status. DISCUSSION: Social integration may carry mental health risks in times of infectious disease outbreaks.

Assessment of a biofluid mechanics-based model for calculating portal pressure in canines.

BACKGROUND: Portal hypertension is a severe complication caused by various chronic liver diseases. The standard methods for detecting portal hypertension (hepatic venous pressure gradient and free portal pressure) are available in only a few hospitals due to their technical difficulty and invasiveness; thus, non-invasive measuring methods are needed. This study aimed to establish and assess a novel model to calculate free portal pressure based on biofluid mechanics. RESULT: Comparison of each dog's virtual and actual free portal pressure showed that a biofluid mechanics-based model could accurately predict free portal pressure (mean difference: -0.220, 95% CI: - 0.738 to 0.298; upper limit of agreement: 2.24, 95% CI: 1.34 to 3.14; lower limit of agreement: -2.68, 95% CI: - 3.58 to - 1.78; intraclass correlation coefficient: 0.98, 95% CI: 0.96 to 0.99; concordance correlation coefficient: 0.97, 95% CI: 0.93 to 0.99) and had a high AUC (0.984, 95% CI: 0.834 to 1.000), sensitivity (92.3, 95% CI: 64.0 to 99.8), specificity (91.7, 95% CI: 61.5 to 99.8), positive likelihood ratio (11.1, 95% CI: 1.7 to 72.8), and low negative likelihood ratio (0.08, 95% CI: 0.01 to 0.6) for detecting portal hypertension. CONCLUSIONS: Our study suggests that the biofluid mechanics-based model was able to accurately predict free portal pressure and detect portal hypertension in canines. With further research and validation, this model might be applicable for calculating human portal pressure, detecting portal hypertensive patients, and evaluating disease progression and treatment efficacy.

Self-Perceptions of Aging and Control of Life in Late Adulthood: Between-Person and Within-Person Associations.

Objectives: This study aimed to examine the longitudinal relationship between two central concepts in aging research-self-perceptions of aging (SPA) and perceived control of life (COL). Method: The data came from three measurement points over a 9-year period in the Health and Retirement Study (HRS). A random intercepts cross-lagged panel model (RI-CLPM) was estimated. Results: The covariations between SPA and COL across 9 years were evident at both the between-person level and the within-person within-time level. The results revealed a reciprocal relationship between SPA and COL: Higher than usual negative SPA predicted within-person decreases in COL 4 years later, and lower than usual COL predicted future within-person increases in negative SPA. Furthermore, SPA were found to have a somewhat larger effect on COL than the corresponding influence of COL on SPA. Discussion: This study enriches the stereotype embodiment theory and the practice by documenting a reciprocal interrelationship between SPA and COL.

Establishment and assessment of the hepatic venous pressure gradient using biofluid mechanics (HVPGBFM): protocol for a prospective, randomised, non-controlled, multicentre study.

INTRODUCTION: Portal hypertension (PH) is a severe disease with a poor outcome. Hepatic venous pressure gradient (HVPG), the current gold standard to detect PH, is available only in few hospitals due to its invasiveness and technical difficulty. This study aimed to establish and assess a novel model to calculate HVPG based on biofluid mechanics. METHODS AND ANALYSIS: This is a prospective, randomised, non-controlled, multicentre trial. A total of 248 patients will be recruited in this study, and each patient will undergo CT, blood tests, Doppler ultrasound and HVPG measurement. The study consists of two independent and consecutive cohorts: original cohort (124 patients) and validation cohort (124 patients). The researchers will establish and improve the HVPG using biofluid mechanics (HVPGBFM)model in the original cohort and assess the model in the validation cohort. ETHICS AND DISSEMINATION: The study was approved by the Scientific Research Projects Approval Determination of Independent Ethics Committee of Shanghai Ninth People's Hospital Affiliated to Shanghai Jiao Tong University School of Medicine (approval number 2017-430 T326). Study findings will be disseminated through peer-reviewed publications and conference presentations. TRIAL REGISTRATION NUMBER: NCT03470389.

Monte Carlo simulation on the dynamics of a semi-flexible polymer in the presence of nanoparticles.

The dynamics of a semi-flexible polymer chain in the presence of periodically distributed nanoparticles is simulated by using off-lattice Monte Carlo simulations. For repulsive or weak attractive nanoparticles, the dynamics are slowed down monotonically by increasing the chain stiffness kθ or decreasing the inter-particle distance d. For strong attractive nanoparticles, however, the dynamics show nonmonotonic behaviors with kθ and d. An interesting result is that a stiff polymer may move faster than a flexible one. The underlying mechanism is that the nanoparticle's attraction is weakened by the chain stiffness. The nonmonotonic behavior of the polymer's dynamics with kθ is explained by the competition between the weakening effect of the chain stiffness on the nanoparticle's attraction and the intrinsic effect of chain stiffness which reduces the dynamics of the polymer. In addition, the nonmonotonic behavior of the polymer's dynamics with d is explained by the competition between the nanoparticle-exchange motion of the polymer dominated at small d and the desorption-and-adsorption motion at large d. The excluded volume effect of the nanoparticles plays a more important role for stiffer polymers as the attraction of the nanoparticles is weakened by the chain stiffness.

Study on the polymer diffusion in a media with periodically distributed nano-sized fillers.

The effect of nano-sized fillers on the equilibrium and dynamical properties of a linear polymer is studied by using off-lattice Monte Carlo simulation. Fillers are arranged periodically in the system with period d and Lennard-Jones interaction between polymer and fillers is considered. Results show that the statistical dimension and dynamical diffusion of the polymer are dependent on the polymer-filler interaction strength ɛ(pf) and the relative size between R(G0) and d, here R(G0) is the radius of gyration of polymer in dilute solution. Normal diffusion of polymer is always observed in the regime 2R(G0) > d. And the diffusion coefficient D is scaled with chain length N as D ~ N(-α), where the exponent α increases with ɛ(pf). Whereas in the regime 2R(G0) < d ≪ Nl0 with l0 the mean bond length of polymer, normal diffusion is observed only at ɛ(pf) < 2, but the polymer will be adsorbed on the fillers and cannot diffuse at ɛ(pf) > 2. In addition, we find that there is a critical interaction strength ɛ*(pf) = 2 in our model system.

Separating different polymers using an interacting nanopore: a Monte Carlo study.

Translocation of a multi-polymer system containing two kinds of polymers, polymer A and polymer B, through an interacting nanopore is studied using dynamic Monte Carlo method. Polymer A and polymer B have different polymer-pore interactions. The probability of one kind of polymer first translocating through a nanopore is dependent on the polymer-pore interactions and the magnitude of driving force for monomers inside the nanopore. At weak driving, there are separation regions where one kind of polymer translocates through the pore always before another kind of polymer. A phase diagram containing separation regions and mixed region is presented. At last, the first-in first-out rule for the polymer translocation is investigated.

Influence of polymer-pore interaction on the translocation of a polymer through a nanopore.

The translocation of a bond fluctuation polymer through an interacting nanopore is studied using dynamic Monte Carlo simulation. A driving force F is applied only for monomers inside the pore. The influence of polymer-pore interaction on the scaling relation τ~N(α) is studied for both unbiased and biased translocations, with τ the translocation time and N the polymer length. Results show that the exponent α is dependent on the polymer-pore interaction. For a noninteracting pore, we find α=2.48 for unbiased translocation and α=1.35 for strong biased translocation; for strong attraction, we find α=2.35 for unbiased translocation and α=1.22 for strong biased translocation. The unbiased translocation corresponds to the low-NF regime whereas the strong biased translocation corresponds to the high-NF regime.

Simulation study on the translocation of a partially charged polymer through a nanopore.

The translocation of a partially charged polymer through a neutral nanopore under external electrical field is studied by using dynamic Monte Carlo method on a simple cubic lattice. One monomer in the polymer is charged and it suffers a driving force when it locates inside the pore. Two time scales, mean first passage time τ(FP) with the first monomer restricted to never draw back into cis side and translocation time τ for polymer continuously threading through nanopore, are calculated. The first passage time τ(FP) decreases with the increase in the driving force f, and the dependence of τ(FP) on the position of charged monomer M is in agreement with the theoretical results using Fokker-Planck equation [A. Mohan, A. B. Kolomeisky, and M. Pasquali, J. Chem. Phys. 128, 125104 (2008)]. But the dependence of τ on M shows a different behavior: It increases with f for M < N/2 with N the polymer length. The novel behavior of τ is explained qualitatively from dynamics of polymer during the translocation process and from the free energy landscape.

Effects of an attractive wall on the translocation of polymer under driving.

The effects of an attractive wall at the trans side on the translocation of an eight-site bond-fluctuation model (BFM) polymer through a pore in a membrane under driving are simulated by the dynamic Monte Carlo method. The attractive wall shows two contrary effects: its excluded volume effect reduces configuration entropy and thus hinders the translocation of the polymer, while its attraction decreases the energy and thus accelerates the translocation. At a critical polymer-wall interaction ε* ≈- 1, we find that the two effects compensate each other and the translocation time τ is roughly independent of the separation distance between the wall and the pore. The value ε* ≈- 1 is roughly equal to the critical adsorption point for the BFM polymer. Moreover, the value of the critical attraction is roughly independent of chain length N and chemical potential difference Δµ. At last, a scaling relation τ âˆ¼ N(α) is observed for polymer translocation at a high value of NΔµ. Though the translocation time is highly dependent on the polymer-wall interaction and pore-wall separation distance, the exponent α is always about 1.30 ± 0.05 so long as NΔµ is large enough.

Monte Carlo simulation on polymer translocation in crowded environment.

The effect of crowded environment with static obstacles on the translocation of a three-dimensional self-avoiding polymer through a small pore is studied using dynamic Monte Carlo simulation. The translocation time τ is dependent on polymer-obstacle interaction and obstacle concentration. The influence of obstacles on the polymer translocation is explained qualitatively by the free energy landscape. There exists a special polymer-obstacle interaction at which the translocation time is roughly independent of the obstacle concentration at low obstacle concentration, and the strength of the special interaction is roughly independent of chain length N. Scaling relation τ ~ N(1.25) is observed for strong driving translocations. The diffusion property of polymer chain is also influenced by obstacles. Normal diffusion is only observed in dilute solution without obstacles or in a crowded environment with weak polymer-obstacle attraction. Otherwise, subdiffusion behavior of polymer is observed.

Escape of polymer chains from an attractive channel under electrical force.

The escape of polymer chains from an attractive channel under external electrical field is studied using dynamical Monte Carlo method. Though the escaping process is nonequilibrium in nature, results show that the one-dimensional diffusion theoretical model based on the equilibrium assumption can describe the dependence of the average escaping time (τ(0)) on the polymer-channel interaction (ɛ), the electrical field (E), the chain length (n), and the channel length (L), qualitatively. Results indicate that both ɛ and E play very important roles in the escaping dynamics. For small ɛ, the polymer chain moves out of the channel continuously and quickly. While for large ɛ, the polymer chain is difficult to move out of long channels as it is trapped for a long time (τ(trap)) when the end segment is near the critical point x(C). These results are consistent with the theoretical results for the free energy profiles at small ɛ and large ɛ, respectively. The dependence of x(C) and τ(trap) on ɛ and E are discussed, and specific relations are obtained. The configurational properties of polymer chain are also investigated during the escaping process.

Simulation study on the translocation of diblock copolymer A(n)B(n) through interacting nanopores.

Translocation of diblock copolymer A(n)B(n) through an interacting nanopore is studied using a dynamic Monte Carlo method on a simple three-dimensional cubic lattice. The probabilities and translocation times of two translocation orientations of copolymer, orientation A with block A translocating first and orientation B with block B first, are mainly dependent on the segment-pore interactions ε(A) and ε(B). We find that both the probability and the translocation time are larger for the orientation with stronger attraction. The dynamic behaviors of copolymer translocation at different ε(A) and ε(B) can be explained based on the free energy landscapes of homopolymer at different polymer-pore interaction. The results reveal a complicated free energy landscape for copolymer translocation.

The critical adsorption point of self-avoiding walks: a finite-size scaling approach.

The critical adsorption of self-avoiding polymer chain in a simple cubic lattice onto a flat surface is studied with Monte Carlo simulations. The dependence of number of surface contacts M on chain length N and polymer-surface interaction epsilon is investigated by a finite-size scaling approach. We estimate the critical adsorption point epsilon(c)=0.291+/-0.002 and the exponent phi=0.54+/-0.01. The asymptotic behaviors M proportional variant N for epsilon>>epsilon(c) and M proportional variant N(0) for epsilon<

Dynamic Monte Carlo study on the probability distribution functions of tail-like polymer chain.

The configurational properties of tail-like polymer chains with one end attached to a flat surface are studied by using dynamic Monte Carlo technique. We find that the probability distribution of the free end in z direction P(R(z)) and the density profile rho(z) can be scaled approximately by a factor beta to be a length independent function for both random walking (RW) and self-avoiding walking (SAW) tail-like chains, where the factor beta is related to the mean square end-to-end distance . The scaled P(R(z)) of the SAW chain roughly overlaps that of the RW chain, but the scaled rho(z) of the SAW chain locates at smaller betaz than that of the RW chain.

[Single-dose ceftriaxone versus multiple-dose cefuroxime for prophylaxis of surgical site infection].

OBJECTIVE: To compare the effects and pharmacoeconomics of single-dose of ceftriaxone versus 3-day cefuroxime prophylaxis in patients undergoing gastric or colorectal resection. METHODS: Three hundred and five consecutive patients with gastric or colorectal cancer from 5 medical centers were randomly divided into ceftriaxone group (n = 153, receiving intravenously 1 g ceftriaxone 0.5 - 1 h prior to operation only) and cefuroxime group (n = 152, receiving 0.75 g cefuroxime preoperatively and the same dose q8h for 3 d). The patients' intra- and postoperative status, adverse responses and infectious complications were observed and documented, and pharmacoeconomic parameters were analyzed. RESULTS: The disease distribution, operative procedures and patients' conditions in the 2 groups were comparable. No adverse responses to the test antibiotics were observed. Postoperative infectious complications occurred in 7 cases in the ceftriaxone group (4.58%) and 14 cases in the cefuroxime group (9.21%), respectively (P = 0.992), among which, 12 cases were surgical site infections (incisional, intra-abdominal): 2 cases in the ceftriaxone group (1.31%), and 10 cases in the cefuroxime group (6.58%), (chi(2) = 5.607, P = 0.018). The direct cost related to prevention and treatment of surgical site infections was 283.5 RMB in the ceftriaxone group and 811.1 RMB in the cefuroxime group (Z = 14.51, P = 0.000). CONCLUSION: Both ceftriaxone and cefuroxime are safe and effective for prevention of surgical site infections. Single-dose ceftriaxone prophylaxis is sufficient for gastric and colorectal operations, with a better cost-effectiveness ratio.