The additive function of YIGE2 and YIGE1 in regulating maize ear length.

Ear length (EL) is a key trait that greatly contributes to yield in maize. Although dozens of EL quantitative trait loci have been mapped, very few causal genes have been cloned, and the molecular mechanisms remain largely unknown. Our previous study showed that YIGE1 is involved in sugar and auxin pathways to regulate ear inflorescence meristem (IM) development and thus affects EL in maize. Here, we reveal that YIGE2, the paralog of YIGE1, regulates maize ear development and EL through auxin pathway. Knockout of YIGE2 causes a significant decrease of auxin level, IM length, floret number, EL, and grain yield. yige1 yige2 double mutants had even shorter IM and ears implying that these two genes redundantly regulate IM development and EL. The genes controlling auxin levels are differential expressed in yige1 yige2 double mutants, leading to lower auxin level. These results elucidated the critical role of YIGE2 and the redundancy between YIGE2 and YIGE1 in maize ear development, providing a new genetic resource for maize yield improvement.

Impacts of oxbow lake evolution on sediment microbial community structure in the Yellow River source region.

Oxbow lake formation and evolution have significant impacts on the fragile Yellow River Basin ecosystem. However, the effects of different oxbow lake evolutionary stages on sediment microbial community structure are not yet understood comprehensively. Therefore, microbial community structure in three stages of oxbow lake succession, namely, lotic lake (early stage), semi-lotic lake (middle stage), and lentic lake (late stage), was investigated in the present study in the Yellow River Basin on the Qinghai-Tibet Plateau. Amplicon sequencing was employed to reveal differences in microbial community diversity and composition. The bacterial and fungal communities in sediment were significantly different among the three succession stages and were driven by different environmental factors. In particular, bacterial community structure was influenced primarily by nitrate-nitrogen (N), microbial biomass phosphorus, and total carbon (C) and organic C in the early, middle, and late stages, respectively. Conversely, fungal community structure was influenced primarily by ammonium-N in the early stage and by moisture content in the middle and late stages. However, the predicted functions of the microbial communities did not exhibit significant differences across the three succession stages. Both bacteria and fungi were influenced significantly by stochastic factors. Homogeneous selection had a high relative contribution to bacteria community assembly in the middle stage, whereas the relative contributions of heterogeneous selection processes to fungal community assembly increased through the three stages. As succession time increased, the total number of keystone species increased gradually, and the late succession stage had high network complexity and the highest network stability. The findings could facilitate further elucidation of the evolution mechanisms of oxbow lake source area, high-altitude river evolution dynamics, in addition to aiding a deeper understanding of the long-term ecological evolution patterns of source river ecosystems.

Tunable Oxygen Vacancies of Cobalt Oxides in Lithium-Oxygen Batteries: Morphology Control of Discharge Product.

The discharge product Li2O2 is difficult to decompose in lithium-oxygen batteries, resulting in poor reversibility and cycling stability of the battery, and the morphology of Li2O2 has a great influence on its decomposition during the charging process. Therefore, reasonable design of the catalyst structure to improve the density of catalyst active sites and make Li2O2 form a morphology which is easy to decompose in the charging process will help improve the performance of battery. Here, we demonstrate a series of hollow nanoboxes stacked by Co3O4 nanoparticles with different sizes. The results show that the surface of the nanoboxes composed of smaller size Co3O4 nanoparticles contains abundant pore structure and higher concentration of oxygen vacancies, which changes the adsorption energy of reactants and intermediates, providing more nucleation sites for Li2O2, thereby forming Li2O2 with high dispersion, which is easier to decompose during charging, and eventually improve the performance of the battery. This provides an important idea for the structural design of the cathode catalyst in lithium-oxygen batteries and the regulation of Li2O2 morphology.

Regulation of DNA-binding activity of the Staphylococcus aureus catabolite control protein A by copper (II)-mediated oxidation.

Catabolite control protein A (CcpA) of the human pathogen Staphylococcus aureus is an essential DNA regulator for carbon catabolite repression and virulence, which facilitates bacterial survival and adaptation to a changing environment. Here, we report that copper (II) signaling mediates the DNA-binding capability of CcpA in vitro and in vivo. Copper (II) catalyzes the oxidation of two cysteine residues (Cys216 and Cys242) in CcpA to form intermolecular disulfide bonds between two CcpA dimers, which results in the formation and dissociation of a CcpA tetramer of CcpA from its cognate DNA promoter. We further demonstrate that the two cysteine residues on CcpA are important for S. aureus to resist host innate immunity, indicating that S. aureus CcpA senses the redox-active copper (II) ions as a natural signal to cope with environmental stress. Together, these findings reveal a novel regulatory mechanism for CcpA activity through copper (II)-mediated oxidation.

Ultrafast vortex arrays generated from a mode-locked oscillator with dispersion management.

Herein, we demonstrate the generation of optical vortex arrays pulses using a Sagnac common-path interferometric vortex generator. Hermite-Gaussian (HG) modes with different orders are initially obtained from a SESAM mode-locked laser in the positive dispersion regime. Then, in the interferometric vortex generator, by controlling the phase difference and sheering displacement between two HG modes, optical vortex pulses with different numbers of phase singularities are generated through superposition. The generated HG10 mode has a pulse width of 2 ps and maximum energy of 0.75 nJ. One-dimensional vortex arrays and triangular vortex arrays are also generated, which are formed by HGm0 and HG0n modes, respectively. This work has potential applications in the massive manipulation of microparticles, optical communication, and so on.

1024-ary composite OAM shift keying for free-space optical communication system decoded by a two-step neural network.

The demand for high-dimensional encoding techniques for communication systems is increasing. Vortex beams carrying orbital angular momentum (OAM) provide new degrees of freedom for optical communication. In this study, we propose an approach for increasing the channel capacity of free-space optical communication systems by integrating superimposed orbital angular momentum (OAM) states and deep learning techniques. We generate composite vortex beams with topological charges ranging from -4 to 8 and radial coefficients ranging from 0 to 3. A phase difference among each OAM state is introduced to significantly increase the number of available superimposed states, achieving up to 1024-ary codes with distinct features. To accurately decode the high-dimensional codes, we propose a two-step convolutional neural network (CNN). The first step is to make a coarse classification of the codes, while the second step is to finely identify the code and achieve decoding. Our proposed method demonstrates 100% accuracy achieved for the coarse classification after 7 epochs, 100% accuracy achieved for the fine identification after 12 epochs, and 99.84% accuracy achieved for testing, which is much faster and more accurate than one-step decoding. To demonstrate the feasibility of our method, we successfully transmitted a 24-bit true-color Peppers image once with a resolution of 64 × 64 in the laboratory, yielding a bit error rate of 0.

Improving the formation probability and stability of noise-like pulse by weakening the spectrum filtering effect.

Noise-like pulses (NLP) are extremely sought after in low-coherence tomography and supercontinuum, etc. Here, we propose an effective method to form the NLP in the all-normal-dispersion (ANDi) fiber laser by weakening the spectrum filtering for the first time. Numerical explorations are performed in detail and demonstrate that the NLP can be originated from the clustering behavior of amplified random sub-pulses led by the saturable absorber. By simulating the pulse-pattern distribution in the two-dimensional parameter space, it is further found that this kind of NLP pattern is widely distributed where are with a weak spectrum filtering. Since, the weaker the filtering, the harder the dissipative system to achieve balance, which helps to avoid the evolution from the pulse cluster to other coherent states and supports the NLP stability. To prove the feasibility experimentally, we built an ANDi fiber laser based on the nonlinear polarization rotating (NPR). The built laser can operate at the stable dissipative soliton (DS) state with a spectrum filter, which also with a 45 nm wavelength tuning performance. Replacing the filter, only NLP with a 40.2 ps pedestal and 237 fs spike can be attained. The experiments agree well with the numerical predictions. This exploration significantly broadens the design possibilities for ultrafast lasers, making them much more accessible to produce desired pulse patterns.

Light scattering control with the two-step focusing method based on neural networks and multi-pixel coding.

Focusing light through scattering media is essential for high-resolution optical imaging and deep penetration. Here, a two-step focusing method based on neural networks (NNs) and multi-pixel coding is proposed to achieve high-quality focusing with theoretical maximum enhancement. In the first step, a single-layer neural network (SLNN) is used to obtain the initial mask, which can be used to focus with a moderate enhancement. In the second step, we use multi-pixel coding to encode the initial mask. The coded masks and their corresponding speckle patterns are used to train another SLNN to get the final mask and achieve high-quality focusing. In this experiment, for a mask of 16 × 16 modulation units, in the case of using 8 pixels in a modulation unit, focus with the enhancement of 40.3 (only 0.44 less than the theoretical value) has been achieved with 3000 pictures (1000 pictures in the first step and 2000 pictures in the second step). Compared with the case of employing only the initial mask and the direct multi-pixel encoded mask, the enhancement is increased by 220% and 24%. The proposed method provides a new idea for improving the focusing effect through the scattering media using NNs.

All-fiber passively Q-switched laser with flat-top beam emissions.

Flat-top beams have plenty of applications in theoretical and applied research, but they are not eigenmodes of the wave equation. Here, we propose an effective strategy for generating flat-top beams in fibers, which originates from the incoherent superposition of orbital angular momentum (OAM) and fundamental (LP01) modes. The designed all-fiber passively Q-switched laser can realize high-quality pulsed flat-top and OAM beam emissions. The normalized root mean square of the flat-top beam is around 4.7%, and the purity of the OAM mode is calculated to be higher than 98%. For the first time to the best of our knowledge, pulsed emission of a flat-top beam is achieved using an all-fiber laser. Moreover, its repetition rate and duration can be controlled by adjusting the pump.

Light-Triggered Nitric Oxide Release by a Photosensitizer to Combat Bacterial Biofilm Infections.

Bacterial biofilms are a serious global health concern, often responsible for persistent infections. New strategies to prevent and treat bacterial infections by eradication of the biofilms are urgently needed. A novel ruthenium-based compound is reported in this study that functions as both a boronic acid-decorated photosensitizer (PS) and a light-triggered nitric oxide (NO) releasing agent. The compound can selectively attach to the bacterial membrane and biofilms and it is highly potent at eradicating Pseudomonas aeruginosa biofilms through the simultaneous release of NO and reactive oxygen species (ROS). The compound, which is more effective than clinical antibiotic tobramycin, also has excellent bacterial specificity and shows no significant cytotoxicity to human cells. The results reveal potential applications of this innovative dual-functional photoactivated ruthenium compound to combat bacterial biofilm infections.

Effects of selenium combined with zinc amendment on zinc fractions and bioavailability in calcareous soil.

Selenium (Se) and zinc (Zn) are two important trace elements for human being and animals. The interaction between Se and Zn on the bioavailability of Zn in soil is still unclear. Therefore, pot experiments exposed to different dosages of zinc sulfate (ZnSO4) (0, 20, and 50 mg/kg soil) and sodium selenite (Na2SeO3) (0, 0.5, 1.0, and 2.5 mg/kg soil) were conducted to investigate the effects of selenite application on Zn bioavailability in calcareous soil and its related mechanisms. The total Zn content of different tissues (roots and shoots) of pak choi (Brassica chinensis L.) and the changes in Zn fraction distribution in soil before planting and after harvest were determined, and the mobility factor (MF) and distribution index (DI) of Zn in soils were calculated. In addition, the Pearson correlation and path analysis were conducted to clarify the relationships between Zn fractions in soil and the Zn uptake of pak choi. Results showed that Se amendment elevated soil Zn bioavailability at appropriate levels of Se and Zn. When 1.0 and 2.5 mg/kg of Se and 20 mg/kg of Zn were applied in soil, the proportion of exchangeable Zn (Ex-Zn) and Zn weakly bound to organic matter (Wbo-Zn) to the total content of Zn was significantly increased by 28.14%-82.52% compared with that of the corresponding single Zn treatment. Therefore, the Zn concentration in the shoots of pak choi was significantly increased by 27.2%-31.1%. High Zn (50 mg/kg) and Se co-amended treatments showed no significantly beneficial effect on the bioavailability of Zn. In addition, the potential available Zn content in soil (weakly bound to organic matter and carbonate bound Zn) and MF and DI values were all positively correlated with the Zn concentrations in pak choi, indicating that these indexes can be used to predict the bioavailability of Zn in soil. This study can provide a good reference for Se and Zn biofortification of plants in calcareous soil.

The Prognostic Value of Serum Neuron Specific Enolase (NSE) and S100B Level in Patients of Acute Spinal Cord Injury.

BACKGROUND The correlation between serum concentration of neuron specific enolase (NSE), S100B, and the prognosis of patients with acute spinal cord injury (ASCI) remains controversial. MATERIAL AND METHODS Sixty patients with confirmed diagnosis of ASCI were recruited for this study from February 2015 to January 2017. The serum level of NSE and S100B were dynamically measured: on the day of injury and for 2 weeks. The 60 cases were divided into Group A (1 or more than 1 ASIA grade improved at 6 months after the injury) and Group B (ASIA grades changed <1 at 6 months after the injury). The serum level of the 2 groups were compared at different time points. And the prognostic value of serum NSE and S100B as biomarkers in patients with ASCI were calculated by Bayes theorem. RESULTS The serum levels of NSE in Groups A and B on the 2nd day of injury reached a peak at 66.80±13.76 g/L and 98.87±20.12 µg/L, respectively, and then declined gradually. On the 14th day of injury, the serum levels of NSE in both groups were 21.23±8.45 and 39.32±16.31 µg/L, respectively, which were much lower than those on the 2nd day (P<0.05). The serum levels of S100B in Groups A and B rose after the injury and reached a peak on the 4th day of injury. Then, the levels declined gradually to 1.14±0.64 and 1.97±0.98 µg/L, respectively, 2 weeks after the injury. Serum levels of NSE and S100B were good biomarkers for predicting the prognosis of ASCI patients with the sensitivity of 74.35% and 71.79%, the specificity of 71.43% and 66.67%. The cutoff value for serum NSE and S100B were 29.07 µg/L and 1.67 µg/L respectively. The AUCs were 0.78 (95% CI: 0.66-0.89) and 0.76 (95% CI: 0.63-0.89) respectively for serum NSE and S100B. CONCLUSIONS Serum levels of NSE and S100B protein can reflect the degree of spinal cord injury and could be potential biomarkers for the prognosis of acute spinal cord injury.

Hepatocyte cocultures with endothelial cells and fibroblasts on micropatterned fibrous mats to promote liver-specific functions and capillary formation capabilities.

The maintenance of hepatocyte phenotype and functions remains as a great challenge in the generation of functional liver tissue and in vitro model for drug metabolism studies. The use of hepatocyte coculture systems plays essential roles in the establishment of cell-cell and cell-extracellular matrix communications similar to native liver tissues. In the current study, micropatterned electrospun fibrous mats were created to load hepatocytes, fibroblasts, and endothelial cells (ECs), which were precisely assembled to establish their spatially controlled coculture for mimicking the in vivo structure of hepatic lobules. Hepatocytes formed compact polyhedral spheroids with an average diameter of 80-100 µm, reorganized actin filaments in the cell-cell contact regions, and well-developed bile canaliculi. Compared with hepatocytes cultured alone, the coculture of hepatocytes with either fibroblasts or ECs led to significantly higher albumin secretion, urea synthesis and cytochrome P-450 expression, which were dramatically improved by the coculture of hepatocytes with both fibroblasts and ECs. The cocultured ECs well spread on patterned regions with little organized filamentous actin, and significantly higher densities and deeper penetration into patterned scaffolds were determined for ECs after coculture with fibroblasts and hepatocytes compared with those after cultured alone or coculture with either fibroblasts or hepatocytes. A Matrigel overlay assay showed that the capabilities of ECs to form capillary tubes were significantly enhanced by micropatterned coculture with fibroblasts and hepatocytes. Thus, the coculture of hepatocytes, fibroblasts, and ECs on micropatterned fibrous mats helps both hepatocytes in the maintenance of hepatic functions and ECs in the formation of capillary-like structures. It is suggested that the micropatterned coculture model described here not only provides functional hepatic tissues for predictions of drug metabolism profiles, but also will enable investigations on more complex and physiological cell-cell communications.

[White matter injury of spinal cord in rats with chronic fluorosis and recovery after defluoridation].

OBJECTIVE: To explore the injury mechanism for white matter of spinal cord and the improvement of function after defluoridation. METHODS: A total of 120 Wistar rats were separated randomly into 4 groups (n = 30 each). High flouriod group received high concentration NaF water (200 mg/L) to establish fluorosis model; control group distilled water; defluoridation group high concentration NaF water (200 mg/L) for 12 weeks and then distilled water for 12 weeks; defluoridation control group. The urinary contents of fluoride were detected at Weeks 4, 8 and 12. The first two groups were sacrificed at Week 12 while the other two groups at Week 24. The spinal cord functions were detected by BBB scale and incline plate test. Their cervical spinal cord tissues were collected and observed under electron microscope. The expression of myelin basic protein (MBP) in thoracic cord was detected by immunohistochemistry and Western blot. The comparison of measurement data was performed with F test and correlation analysis. Cytological changes of white matter in spinal cord were detected after chronic fluorosis. RESULTS: The spinal functions of high flouriod and defluoridation groups were inferior to those of the control groups. But no difference existed among the groups. Pathological manifestations of chronic white matter injury of spinal cord could be found in high flouriod and defluoridation groups. The MBP expression in spinal cord of fluorosis and defluoridation groups decreased in comparison with those in control groups. But no difference existed among them. CONCLUSION: White matter injury of spinal cord is present in chronic fluorosis rats. Defluoridation for a short time offers no recovery.

Blue-emitting tryptophan-protected gold nanoclusters acted as a sensitive nanosensor for fluorescence sensing and visual imaging detection of furaltadone.

Herein, blue-emitting gold nanoclusters (Au NCs) were carried out through tryptophan as the protecting and reducing agents. In aqueous solution of Au NCs@tryptophan, the addition of furaltadone guaranteed the interaction of furaltadone with tryptophan around Au NCs. The propinquity of furaltadone to Au NCs caused that the fluorescence of Au NCs was weakened by furaltadone based on the inner filter effect (IFE). Under the optimal measurement conditions, the logarithm of relative fluorescence intensity of Au NCs@tryptophan was linearly carried out with the furaltadone amount increasing from 0.5 to 100 µM, the corresponding detection limit was 0.087 µM. The fluorescence change of Au NCs@tryptophan displayed excellent selectivity and sensitivity for furaltadone than other possible substance in the human body. In view of Au NCs@tryptophan, the as-performed fluorescence nanosensor suggested outstanding ability for furaltadone sensing in real samples. Obviously, this nanoprobe of furaltadone could implement the naked-eye visual fluorescence determination of furaltadone.

Synergy of Pd2+/S2--Doped TiO2 Supported on 2-Methylimidazolium-Functionalized Polypyrrole/Graphene Oxide for Enhanced Nitrogen Electrooxidation.

The electrosynthesis of nitrate catalyzed by electrochemical nitrogen oxidation reaction (NOR) is considered as an alternative and sustainable approach to the conventional industrial manufacture, but optimizing the electrocatalytic NOR performance and fabricating the efficient NOR electrocatalysts at the design level still encounter great challenges. Herein, unique Pd2+- and S2--doped TiO2 (Pb/S-TiO2) nanoparticles are successfully in situ grown on the surface of 2-methylimidazolium-functionalized polypyrrole/graphene oxide (2-MeIm/PPy/GO), which present the typical hierarchical micro-nanostructures, resulting in the excellent electrocatalytic NOR performance with the highest NO3 - yield of 72.69 µg h-1 mg-1 act. and the maximum Faraday efficiency of 8.92% at 2.04 V (vs reversible hydrogen electrode) due to the synergistic effect of each component. Due to the doping effect, the appropriate oxygen evolution reaction (OER) activity is achieved by Ti-site, where OER principally occurs, providing *O during the non-electrochemical step of NOR, while the electrocatalytic NOR process as the electrochemical conversion of inert N2 to active *NO intermediates mainly occurs at the Pd-site. Especially, the sulfate radicals in situ formed on Pb/S-TiO2@2-MeIm/PPy/GO further promote nitrogen adsorption and decrease the reaction energy barrier, resulting in the acceleration of NOR. It provides theoretical and practical experience for the design and preparation of NOR electrocatalysts.

Circumventing the activity-selectivity trade-off via the confinement effect from induced potential barriers on the Pd nanoparticle surface.

The request for both high catalytic selectivity and high catalytic activity is rather challenging, particularly for catalysis systems with the primary and side reactions having comparable energy barriers. Here in this study, we simultaneously optimized the selectivity and activity for acetylene semi-hydrogenation by rationally and continuously varying the doping ratio of Zn atoms on the surface of Pd particles in Pd/ZnO catalysts. In the reaction temperature range of 40-200 °C, the conversion of acetylene was close to ∼100%, and the selectivity for ethylene exceeded 90% (the highest ethylene selectivity, ∼98%). Experimental characterization and density functional theory calculations revealed that the Zn promoter could alter the catalyst's potential energy surface, resulting in a "confinement" effect, which effectively improves the selectivity yet without significantly impairing the catalytic activity. The mismatched impacts on activity and selectivity resulting from continuous and controllable alteration in the catalyst structure provide a promising parameter space within which the two aspects could both be optimized.

Causal relationship between rheumatoid arthritis and epilepsy in a European population: a univariate and multivariate Mendelian randomization study.

Background: Several previous studies have reported an association between rheumatoid arthritis (RA) and epilepsy, but the causal relationship is unclear. The aim of this study was to assess the connection between RA and epilepsy in a European population using Mendelian randomization (MR). Methods: Genome-wide association study summary data on RA and epilepsy from European populations were included. Univariate MR (UVMR) and multivariate MR were used to investigate the causal relationship between the two conditions. Three analysis methods were applied: inverse variance weight (IVW), MR-Egger, and weighted median, with IVW being the primary method. Cochran Q statistics, MR-PRESSO, MR-Egger intercept, leave-one-out test, and MR-Steiger test were combined for the sensitivity analysis. Results: UVMR showed a positive association between RA and epilepsy risk (OR=1.038, 95% CI=1.007-1.038, p=0.017) that was supported by sensitivity analysis. Further MVMR after harmonizing the three covariates of hypertension, alcohol consumption, and smoking, confirmed the causal relationship between RA and epilepsy (OR=1.049, 95% CI=1.011-1.087, p=0.010). Conclusion: This study demonstrated that RA is associated with an increased risk of epilepsy. It has emphasized that the monitoring of epilepsy risk in patients diagnosed with RA should be strengthened in clinical practice, and further studies are needed in the future to explore the potential mechanism of action connecting the two conditions.

Early statin exposure influences cardiac and skeletal development with implications for ion channel transcriptomes in zebrafish.

Statins, widely prescribed for cholesterol management by inhibiting HMG-CoA reductase in the cholesterol biosynthesis pathway, may also influence vertebrate development. In this study, we investigated the developmental effects of two widely used statins, atorvastatin (ATO) and pravastatin (PRA), on zebrafish offspring. For ATO, we administered doses classified as low (1 µM), medium (5 µM), and high (10 µM), while for PRA, the corresponding concentrations were set at low (18 µM), medium (180 µM), and high (270 µM). Our results showed significant reductions in birth and hatching rates, along with decreased body length in offspring at all ATO concentrations and medium to high PRA concentrations. A notable increase in malformation rates, especially in the spine and heart, was observed across all ATO treatments and in medium and high PRA groups. Additionally, we observed reduced heart contraction rates, decreased heart size, lower bone volumes, and diminished expression of mRNA osteogenic markers. Elevated venous sinus-artery bulb (SV-BA) ratios, increased thoracic area, and abnormal cartilage development were also prominent in all ATO-treated groups. Transcriptome analysis revealed alterations in genes predominantly associated with ion channels. These findings provide insights into the potential impacts of specific concentrations of statins on offspring development and highlight potential gene interactions with statins.

[Etiology and treatment of postoperative spinal cord injury for patients undergoing laminectomy for fluorosis thoracic canal stenosis].

OBJECTIVE: To elucidate the etiology of postoperative spinal cord injury (PSCI) for patients undergoing laminectomy for fluorosis thoracic canal stenosis (FTCS) and summarize the methods of diagnosis and treatment. METHODS: From 2006 to 2009, a total of 192 FTCS cases underwent laminectomy. Among them, 16 cases with gradual postoperative neural deterioration were finally diagnosed as PSCI on MRI.One case of intraoperative spinal cord injury was excluded so that only 15 cases were included. RESULTS: All cases were treated immediately with incision cite puncture and dehydration.Neural function recovered after secondary operation as JOA score improved from 3.00 ± 1.14 to 7.72 ± 1.41 at 12 months follow-up.Statistical analysis demonstrated a linear correlation between the diagnosis time and the improvement of JOA score. CONCLUSION: Hematoma and fluid leakage are the common reasons of PSCI for FTCS patients. Meticulous hemostasis, usage of artificial dura matter and partial negative pressure drainage are valuable preventive measures.