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1.
Children (Basel) ; 11(5)2024 Apr 23.
Article in English | MEDLINE | ID: mdl-38790500

ABSTRACT

BACKGROUND: Infants presenting with unexpected pneumoperitoneum upon abdominal X-ray, indicating a gastrointestinal perforation (GIP), have a surgical emergency with potential morbidity and mortality. Preoperative determination of the location of perforation is challenging but will aid the surgeon in optimizing the surgical strategy, as colon perforations are more challenging than small bowel perforations. Therefore, the aim of this study is to provide an overview of preoperative patient characteristics, determine the differences between the small bowel and colon, and determine underlying causes in a cohort of infants with unexpected GIP. METHODS: All infants (age ≤ 6 months) who presented at our center with unexpected pneumoperitoneum (no signs of pneumatosis before) undergoing surgery between 1996 and 2024 were retrospectively included. The differences between the location of perforation were analyzed using chi-squared and t-tests. Bonferroni correction was used to adjust for multiple tests. RESULTS: In total, 51 infants presented with unexpected pneumoperitoneum at our center, predominantly male (N = 36/51) and premature (N = 40/51). Among them, twenty-six had small bowel, twenty-two colon, and three stomach perforations. Prematurity (p = 0.001), birthweight < 1000 g (p = 0.001), respiratory support (p = 0.001), and lower median arterial pH levels (p = 0.001) were more present in patients with small bowel perforation compared with colon perforations. Pneumatosis intestinalis was more present in patients with colon perforation (p = 0.004). All patients with Hirschsprung disease and cystic fibrosis had colon perforation. The final diagnoses were mainly focal intestinal perforations (N = 27/51) and necrotizing enterocolitis (N = 9/51). CONCLUSIONS: Infants with unexpected GIP, birthweight < 1000 g, and prematurity have more risk for small bowel perforation. In case of colon perforation, additional screening (for Hirschsprung and cystic fibrosis) should be considered.

2.
Chemphyschem ; : e202400154, 2024 May 26.
Article in English | MEDLINE | ID: mdl-38798029

ABSTRACT

Turning waste into valuable products is one of the main challenges of the chemical industry. In this work, chitosan (CS), an abundant, low-cost, and non-toxic biopolymer derived from chitin, was reshaped into beads of ~3 mm. Their suitability as a support material for active phase catalyst materials was tested for a zirconium-based Metal-Organic Framework (MOF) with incorporated Pt, namely UiO-67-Pt. Its incorporation was investigated via two procedures: a one-pot synthesis (OPS) and a post-synthetic functionalization (PSF) synthesis method. Scanning electron microscopy (SEM) images show good UiO-67-Pt dispersion throughout the CS beads for the one-pot synthesized material (UiO-67-Pt-OPS@CS). However, this uniform dispersion was not observed for the post-synthetically functionalized material (UiO-67-Pt-PSF@CS). The success of the implementation of UiO-67-Pt was evaluated with ultraviolet-visible and infrared spectroscopy for both composite materials. Thermogravimetric analysis (TGA) reveals higher thermal stabilities for UiO-67-Pt-OPS@CS composite beads in comparison to pure CS beads, but not for UiO-67-Pt-PSF@CS. The study provides valuable insights into the potential of chitosan as a green, bead-shaped support material for MOFs, offering flexibility in their incorporation through different synthesis routes. It further contributes to the broader goal of the sustainable and eco-friendly design of a new generation of catalysts made from waste materials, which will be the topic of future studies.

3.
Nat Commun ; 15(1): 4517, 2024 May 28.
Article in English | MEDLINE | ID: mdl-38806479

ABSTRACT

Networks of nanowires, nanotubes, and nanosheets are important for many applications in printed electronics. However, the network conductivity and mobility are usually limited by the resistance between the particles, often referred to as the junction resistance. Minimising the junction resistance has proven to be challenging, partly because it is difficult to measure. Here, we develop a simple model for electrical conduction in networks of 1D or 2D nanomaterials that allows us to extract junction and nanoparticle resistances from particle-size-dependent DC network resistivity data. We find junction resistances in porous networks to scale with nanoparticle resistivity and vary from 5 Ω for silver nanosheets to 24 GΩ for WS2 nanosheets. Moreover, our model allows junction and nanoparticle resistances to be obtained simultaneously from AC impedance spectra of semiconducting nanosheet networks. Through our model, we use the impedance data to directly link the high mobility of aligned networks of electrochemically exfoliated MoS2 nanosheets (≈ 7 cm2 V-1 s-1) to low junction resistances of ∼2.3 MΩ. Temperature-dependent impedance measurements also allow us to comprehensively investigate transport mechanisms within the network and quantitatively differentiate intra-nanosheet phonon-limited bandlike transport from inter-nanosheet hopping.

4.
J Appl Crystallogr ; 57(Pt 2): 481-491, 2024 Apr 01.
Article in English | MEDLINE | ID: mdl-38596732

ABSTRACT

The strong metal-support interaction (SMSI) is a phenomenon observed in supported metal catalyst systems in which reducible metal oxide supports can form overlayers over the surface of active metal nanoparticles (NPs) under a hydrogen (H2) environment at elevated temperatures. SMSI has been shown to affect catalyst performance in many reactions by changing the type and number of active sites on the catalyst surface. Laboratory methods for the analysis of SMSI at the nanoparticle-ensemble level are lacking and mostly based on indirect evidence, such as gas chemisorption. Here, we demonstrate the possibility to detect and characterize SMSIs in Co/TiOx model catalysts using the laboratory X-ray standing wave (XSW) technique for a large ensemble of NPs at the bulk scale. We designed a thermally stable MoNx/SiNx periodic multilayer to retain XSW generation after reduction with H2 gas at 600°C. The model catalyst system was synthesized here by deposition of a thin TiOx layer on top of the periodic multilayer, followed by Co NP deposition via spare ablation. A partial encapsulation of Co NPs by TiOx was identified by analyzing the change in Ti atomic distribution. This novel methodological approach can be extended to observe surface restructuring of model catalysts in situ at high temperature (up to 1000°C) and pressure (≤3 mbar), and can also be relevant for fundamental studies in the thermal stability of membranes, as well as metallurgy.

5.
J Phys Chem C Nanomater Interfaces ; 128(9): 3693-3702, 2024 Mar 07.
Article in English | MEDLINE | ID: mdl-38476826

ABSTRACT

We present a theoretical model to compute the efficiency of the generation of two or more electron-hole pairs in a semiconductor by the absorption of one photon via the process of carrier multiplication (CM). The photogeneration quantum yield of electron-hole pairs is calculated from the number of possible CM decay pathways of the electron and the hole. We apply our model to investigate the underlying cause of the high efficiency of CM in bulk 2H-MoTe2, as compared to bulk PbS and PbSe. Electronic band structures were calculated with density functional theory, from which the number of possible CM decay pathways was calculated for all initial electron and hole states that can be produced at a given photon energy. The variation of the number of CM pathways with photon energy reflects the dependence of experimental CM quantum yields on the photon energy and material composition. We quantitatively reproduce experimental CM quantum yields for MoTe2, PbS, and PbSe from the calculated number of CM pathways and one adjustable fit parameter. This parameter is related to the ratio of Coulomb coupling matrix elements and the cooling rate of the electrons and holes. Large variations of this fit parameter result in small changes in the modeled quantum yield for MoTe2, which confirms that its high CM efficiency can be mainly attributed to its extraordinary large number of CM pathways. The methodology of this work can be applied to analyze or predict the CM efficiency of other materials.

6.
ChemSusChem ; 17(13): e202301426, 2024 Jul 08.
Article in English | MEDLINE | ID: mdl-38373235

ABSTRACT

Although biomass-based alternatives for the manufacturing of bioplastic films are an important aspect of a more sustainable future, their physicochemical properties need to be able to compete with the existing market to establish them as a viable alternative. One important factor that is often neglected is the long-term stability of renewables-based functional materials, as they should neither degrade after a day or week, nor last forever. One material showing high potential in this regard, also due to its intrinsic biodegradability and antibacterial properties, is chitosan, which can form stable, self-standing films. We previously showed that green additives introduce a broad tunability of the chitosan-based material properties. In this work, we investigate the long-term stability and related degradation processes of chitosan-based bioplastics by assessing their physicochemical properties over 400 days. It was found that the film properties change similarly for samples stored in the fridge (4 °C, dark) as at ambient conditions (20 °C, light/dark cycles of the day). Additives with high vapor pressure, such as glycerol, evaporate and degrade, causing both brittleness and discoloration. In contrast, films with the addition of crosslinking additives, such as citric acid, show high stability also over a long time, bearing great preconditions for practical applications. This knowledge serves as a stepping-stone to utilizing chitosan as an alternative material for renewable-resourced bioplastic products.

7.
J Phys Chem Lett ; 14(49): 11168-11176, 2023 Dec 14.
Article in English | MEDLINE | ID: mdl-38055348

ABSTRACT

In this Perspective, we provide an overview of recent advances in harvesting triplets for photovoltaic and photon upconversion applications from two angles. In singlet fission-sensitized solar cells, the triplets are harvested through a low band gap semiconductor such as Si. Recent literature has shown how a thin interlayer or orientation of the singlet fission molecule can successfully lead to triplet transfer. On the other hand, the integration of transition metal dichalcogenides (TMDCs) with suitable organic molecules has shown triplet-triplet annihilation upconversion (TTA-UC) of near-infrared photons. We consider the theoretical aspect of the triplet transfer process between a TMDC and organic semiconductors. We discuss possible bottlenecks that can limit the harvesting of energy from triplets and perspectives to overcome these.

8.
Int J Gynaecol Obstet ; 163(3): 1018-1023, 2023 Dec.
Article in English | MEDLINE | ID: mdl-37703057

ABSTRACT

OBJECTIVE: We provide an overview of the safety of messenger RNA and inactivated coronavirus disease 2019 (COVID-19) vaccine and monitoring of pregnant women after COVID-19 vaccination. The vaccine safety outcome profile is beneficial for further recommendations of COVID-19 vaccination in pregnancy. METHODS: This research was conducted as descriptive research. Sampling was performed using an online questionnaire to be filled out voluntarily and distributed to all pregnant women in Indonesia who received the COVID-19 vaccination. Data collection was performed and descriptive statistics were obtained. RESULTS: Among 31 977 pregnant women, 24 212 (75.7%) received the first dose, 7619 (23.8%) received the second dose, and 146 (4.5%) received the third dose of the COVID-19 vaccine. Sinovac vaccine is the most administered vaccine to pregnant women (27 122 [84%]). Most pregnant women (78.7%) who were vaccinated had no adverse effects after immunization, while the most reported adverse effects were mild symptoms. CONCLUSION: The current study contributed evidence that COVID-19 vaccination during pregnancy has minimal adverse effects. These findings may help pregnant women and healthcare providers to make informed decisions regarding vaccination.


Subject(s)
COVID-19 Vaccines , COVID-19 , Pregnancy , Female , Humans , COVID-19 Vaccines/adverse effects , COVID-19/prevention & control , Indonesia/epidemiology , Pregnant Women , Vaccination
9.
World J Pediatr Surg ; 6(4): e000565, 2023.
Article in English | MEDLINE | ID: mdl-37671119

ABSTRACT

Objective: Little is known about intestinal anastomotic leakage and stenosis in young children (≤3 years of age). The purpose of this study is to answer the following questions: (1) what is the incidence of anastomotic stenosis and leakage in infants? (2) which surgical diseases entail the highest incidence of anastomotic stenosis and leakage? (3) what are perioperative factors associated with anastomotic stenosis and leakage? Methods: Patients who underwent an intestinal anastomosis during primary abdominal surgery in our tertiary referral centre between 1998 and 2018 were retrospectively included. Both general incidence and incidence per disease of anastomotic complications were determined. Technical risk factors (location and type of anastomosis, mode of suturing, and suture resorption time) were evaluated by multivariate Cox regression for anastomotic stenosis. Gender and American Society of Anaesthesiology (ASA) score of ≥III were evaluated by χ2 test for anastomotic leakage. Results: In total, 477 patients underwent an anastomosis. The most prominent diseases are intestinal atresia (30%), Hirschsprung's disease (29%), and necrotizing enterocolitis (14%). Anastomotic stenosis developed in 7% (34/468) of the patients with highest occurrence in necrotizing enterocolitis (14%, 9/65). Colonic anastomosis was associated with an increased risk of anastomotic stenosis (hazard ratio (HR) =3.6, 95% CI 1.8 to 7.5). No technical features (type of anastomosis, suture resorption time and mode of suturing) were significantly associated with stenosis development. Anastomotic leakage developed in 5% (22/477) of the patients, with the highest occurrence in patients with intestinal atresia (6%, 9/143). An ASA score of ≥III (p=0.03) and male gender (p=0.03) were significantly associated with anastomotic leakage. Conclusions: Both anastomotic stenosis and leakage are major surgical complications. Identifying more patient specific factors can result in better treatment selection, which should not solely be based on the type of disease.

10.
ACS Photonics ; 10(9): 3115-3123, 2023 Sep 20.
Article in English | MEDLINE | ID: mdl-37743944

ABSTRACT

Rhenium disulfide, a member of the transition metal dichalcogenide family of semiconducting materials, is unique among 2D van der Waals materials due to its anisotropy and, albeit weak, interlayer interactions, confining excitons within single atomic layers and leading to monolayer-like excitonic properties even in bulk crystals. While recent work has established the existence of two stacking modes in bulk, AA and AB, the influence of the different interlayer coupling on the excitonic properties has been poorly explored. Here, we use polarization-dependent optical measurements to elucidate the nature of excitons in AA and AB-stacked rhenium disulfide to obtain insight into the effect of interlayer interactions. We combine polarization-dependent Raman with low-temperature photoluminescence and reflection spectroscopy to show that, while the similar polarization dependence of both stacking orders indicates similar excitonic alignments within the crystal planes, differences in peak width, position, and degree of anisotropy reveal a different degree of interlayer coupling. DFT calculations confirm the very similar band structure of the two stacking orders while revealing a change of the spin-split states at the top of the valence band to possibly underlie their different exciton binding energies. These results suggest that the excitonic properties are largely determined by in-plane interactions, however, strongly modified by the interlayer coupling. These modifications are stronger than those in other 2D semiconductors, making ReS2 an excellent platform for investigating stacking as a tuning parameter for 2D materials. Furthermore, the optical anisotropy makes this material an interesting candidate for polarization-sensitive applications such as photodetectors and polarimetry.

11.
ChemSusChem ; 16(20): e202300585, 2023 Oct 20.
Article in English | MEDLINE | ID: mdl-37549200

ABSTRACT

To switch to alternatives for fossil-fuel-based polymer materials, renewable raw materials from green resources should be utilized. Chitosan is such a material that is a strong, but workable derivative from chitin, obtained from crustaceans. However, various applications ask for specific plastic properties, such as certain flexibility, hardness and transparency. With different additives, also obtainable from green resources, chitosan-based composites in the form of self-supporting films, ranging from very hard and brittle to soft and flexible were successfully produced. The additives turned out to belong to one of three categories, namely linear, non-linear, or crosslinking additives. The non-linear additives could only be taken up to a certain relative amount, whereas the uptake of linear additives was not limited within the range of our experiments. Additives with multiple functional groups tend to crosslink chitosan even at room temperature in an acidic medium. Finally, it was shown that dissolving the chitosan in acetic acid and subsequently drying the matrix as a film results in reacetylation compared to the starting chitosan source, resulting in a harder material. With these findings, it is possible to tune the properties of chitosan-based polymer materials, making a big step towards application of this renewable polymer within consumer goods.

12.
Am J Otolaryngol ; 44(5): 103861, 2023.
Article in English | MEDLINE | ID: mdl-37454553

ABSTRACT

INTRODUCTION: Midline neck swellings are very common in children and mostly caused by thyroglossal duct cysts (TGDCs) or dermoid cysts (DCs). Since DCs can undergo simple excision, whilst TGDCs demand more thorough resection via Sistrunk procedure, it is important to differentiate between both pre-operatively. Previous studies have suggested an ultrasound-score (SIST) based on presence of septae, wall irregularity and solid components could do so. This study aims to evaluate the diagnostic accuracy of this score. METHODS: All patients (≤18 years) undergoing surgery between 2006 and 2018 for a midline neck mass at our tertiary centre with a histopathological diagnosis of TGDC or DC were retrospectively included. The pre-operative ultrasound was evaluated by an experienced radiologist and the SIST as well as location, tract, echogenicity, margin and multilocularity were scored. RESULTS: We included 97 children, of whom 67 (69 %) with TGDCs. The SIST showed a sensitivity of 37 %, specificity of 97 %, a positive predictive value of 96 % and a negative predictive value of 35 % for the SIST-score in detecting TGDCs, which resulted in an AUC of 0.67. In addition, internal echogenicity (P < 0.01) and margin definition (P < 0.01) were significantly associated to TGDC diagnosis whilst location and multilocularity were deemed insignificant following Bonferroni correction. CONCLUSION: We conclude that the SIST-score seems very capable to rule in TGDC. However, the SIST-score is far from making a clear distinction between DC and TGDCs preoperatively. The addition of other ultrasound variables, such as margin definition and echogenicity, might increase the diagnostic accuracy and demands further research.


Subject(s)
Dermoid Cyst , Thyroglossal Cyst , Child , Humans , Retrospective Studies , Thyroglossal Cyst/diagnostic imaging , Thyroglossal Cyst/surgery , Dermoid Cyst/diagnostic imaging , Dermoid Cyst/surgery , Dermoid Cyst/pathology , Ultrasonography/methods , Thyroid Gland/pathology
13.
Obes Surg ; 33(8): 2317-2323, 2023 08.
Article in English | MEDLINE | ID: mdl-37347399

ABSTRACT

INTRODUCTION: Same-day discharge (SDD) after bariatric surgery is increasingly being performed and is safe with careful patient selection. However, detecting early complications during the first postoperative days can be challenging. We developed a postoperative care protocol for these patients and aimed to evaluate its effectiveness in detecting complications and monitoring patient recovery. METHODS: A single-center retrospective observational study was conducted with patients with who underwent Roux-en-Y Gastric Bypass (RYGB) with successful SDD. The study evaluated the effectiveness of the safety net that included simple remote monitoring with a pulsoximeter and thermometer, a phone consultation on postoperative day (POD) 1, and a physical consultation on POD 2-4. Furthermore, an analysis was performed on various factors including pain scores, painkiller usage, and incidences of nausea and vomiting on POD 1. RESULTS: In this study, 373 consecutive patients were included, of whom 19 (5.1%) were readmitted until POD 4. Among these, 12 patients (3.2%) reached out to the hospital themselves, while 7 (1.9%) were readmitted after phone or physical consultations. Ten of the readmitted patients had tachycardia. On POD 1, the mean numeric rating scale was 4 ± 2, and 96.6% of the patients used acetaminophen, 35.5% used naproxen, and 9.7% used oxynorm. Of the patients, 13.9% experienced nausea and 6.7% reported vomiting. CONCLUSION: A postoperative care protocol for SDD after RYGB, comprising simple remote monitoring along with a phone consultation on POD 1 and a physical checkup on POD 2-4, was effective in monitoring patient recovery and detecting all early complications.


Subject(s)
Gastric Bypass , Obesity, Morbid , Humans , Gastric Bypass/adverse effects , Gastric Bypass/methods , Nausea/surgery , Obesity, Morbid/surgery , Observational Studies as Topic , Patient Discharge , Postoperative Care , Postoperative Complications/epidemiology , Retrospective Studies , Vomiting
14.
J Chem Phys ; 158(12): 124124, 2023 Mar 28.
Article in English | MEDLINE | ID: mdl-37003779

ABSTRACT

A semiclassical theory of small oscillations is developed for nuclei that are subject to velocity-dependent forces in addition to the usual interatomic forces. When the velocity-dependent forces are due to a strong magnetic field, novel effects arise-for example, the coupling of vibrational, rotational, and translational modes. The theory is first developed using Newtonian mechanics and we provide a simple quantification of the coupling between these types of modes. We also discuss the mathematical structure of the problem, which turns out to be a quadratic eigenvalue problem rather than a standard eigenvalue problem. The theory is then re-derived using the Hamiltonian formalism, which brings additional insight, including a close analogy to the quantum-mechanical treatment of the problem. Finally, we provide numerical examples for the H2, HT, and HCN molecules in a strong magnetic field.

15.
Sci Rep ; 13(1): 6337, 2023 Apr 18.
Article in English | MEDLINE | ID: mdl-37072513

ABSTRACT

We analyze the topology, dispersion, and optical selection rules of bulk Wannier excitons in nanosheets of Bi2Se3, a topological insulator in the family of the bismuth chalcogenides. Our main finding is that excitons also inherit the topology of the electronic bands, quantified by the skyrmion winding numbers of the constituent electron and hole pseudospins as a function of the total exciton momentum. The excitonic bands are found to be strongly indirect due to the band inversion of the underlying single-particle model. At zero total momentum, we predict that the s-wave and d-wave states of two exciton families are selectively bright under left- or right-circularly polarized light. We furthermore show that every s-wave exciton state consists of a quartet with a degenerate and quadratically dispersing nonchiral doublet, and a chiral doublet with one linearly dispersing mode as in transition metal dichalcogenides. Finally, we discuss the potential existence of topological edge states of chiral excitons arising from the bulk-boundary correspondence.

16.
J Chem Phys ; 158(11): 114115, 2023 Mar 21.
Article in English | MEDLINE | ID: mdl-36948801

ABSTRACT

In an ultrastrong magnetic field, with field strength B ≈ B0 = 2.35 × 105 T, molecular structure and dynamics differ strongly from that observed on the Earth. Within the Born-Oppenheimer (BO) approximation, for example, frequent (near) crossings of electronic energy surfaces are induced by the field, suggesting that nonadiabatic phenomena and processes may play a more important role in this mixed-field regime than in the weak-field regime on Earth. To understand the chemistry in the mixed regime, it therefore becomes important to explore non-BO methods. In this work, the nuclear-electronic orbital (NEO) method is employed to study protonic vibrational excitation energies in the presence of a strong magnetic field. The NEO generalized Hartree-Fock theory and time-dependent Hartree-Fock (TDHF) theory are derived and implemented, accounting for all terms that result as a consequence of the nonperturbative treatment of molecular systems in a magnetic field. The NEO results for HCN and FHF- with clamped heavy nuclei are compared against the quadratic eigenvalue problem. Each molecule has three semi-classical modes owing to the hydrogen-two precession modes that are degenerate in the absence of a field and one stretching mode. The NEO-TDHF model is found to perform well; in particular, it automatically captures the screening effects of the electrons on the nuclei, which are quantified through the difference in energy of the precession modes.

17.
Pediatr Surg Int ; 39(1): 160, 2023 Mar 26.
Article in English | MEDLINE | ID: mdl-36967411

ABSTRACT

BACKGROUND: Cardiac anomalies occur frequently in patients with congenital duodenal obstruction (DO). However, the exact occurrence and the type of associated anomalies remain unknown. Therefore, the aim of this systematic review is to aggregate the available literatures on cardiac anomalies in patients with DO. METHODS: In July 2022, a search was performed in PubMed and Embase.com. Studies describing cardiac anomalies in patients with congenital DO were considered eligible. Primary outcome was the pooled percentage of cardiac anomalies in patients with DO. Secondary outcomes were the pooled percentages of the types of cardiac anomalies, type of DO, and trisomy 21. A meta-analysis was performed to pool the reported data. RESULTS: In total, 99 publications met our eligibility data, representing 6725 patients. The pooled percentage of cardiac anomalies was 29% (95% CI 0.26-0.32). The most common cardiac anomalies were persistent foramen ovale 35% (95% CI 0.20-0.54), ventricular septal defect 33% (95% CI 0.24-0.43), and atrial septal defect 33% (95% CI 0.26-0.41). The most prevalent type of obstruction was type 3 (complete atresias), with a pooled percentage of 54% (95% CI 0.48-0.60). The pooled percentage of Trisomy 21 in patients with DO was 28% (95% CI 0.26-0.31). CONCLUSION: This review shows cardiac anomalies are found in one-third of the patients with DO regardless of the presence of trisomy 21. Therefore, we recommend that patients with DO should receive preoperative cardiac screening. LEVEL OF EVIDENCE: II.


Subject(s)
Down Syndrome , Duodenal Obstruction , Heart Defects, Congenital , Humans , Child , Down Syndrome/complications , Down Syndrome/epidemiology , Duodenal Obstruction/congenital , Heart Defects, Congenital/complications , Heart Defects, Congenital/epidemiology
18.
J Phys Chem C Nanomater Interfaces ; 127(4): 1899-1907, 2023 Feb 02.
Article in English | MEDLINE | ID: mdl-36761230

ABSTRACT

We studied the initial nature and relaxation of photoexcited electronic states in CdSe nanoplatelets (NPLs). Ultrafast transient optical absorption (TA) measurements were combined with the theoretical analysis of the formation and decay of excitons, biexcitons, free charge carriers, and trions. In the latter, photons and excitons were treated as bosons and free charge carriers as fermions. The initial quantum yields of heavy-hole (HH) excitons, light-hole (LH) excitons, and charge carriers vary strongly with photon energy, while thermal relaxation occurs always within 1 ps. After that, the population of LH excitons is negligible due to relaxation to HH excitons or decay into free electrons and holes. Up to the highest average number of about four absorbed photons per NPL in our experiments, we found no signatures of the presence of biexcitons or larger complexes. Biexcitons were only observed due to the interaction of a probe-generated exciton with an exciton produced previously by the pump pulse. For higher pump photon energies, the initial presence of more free charge carriers leads to formation of trions by probe photons. On increasing the number of absorbed pump photons in an NPL, the yield of excitons becomes higher as compared to free charge carriers, since electron-hole recombination becomes more likely. In addition to a TA absorption feature at energy below the HH exciton peak, we also observed a TA signal at the high-energy side of this peak, which we attribute to formation of LH-HH biexcitons or trions consisting of a charge and LH exciton.

19.
J Chem Theory Comput ; 19(4): 1231-1242, 2023 Feb 28.
Article in English | MEDLINE | ID: mdl-36705605

ABSTRACT

The Berry curvature is essential in Born-Oppenheimer molecular dynamics, describing the screening of the nuclei by the electrons in a magnetic field. Parts of the Berry curvature can be understood as the external magnetic field multiplied by an effective charge so that the resulting Berry force behaves like a Lorentz force during the simulations. Here, we investigate whether these effective charges can provide insight into the electronic structure of a given molecule or, in other words, whether we can perform a population analysis based on the Berry curvature. To develop our approach, we first rewrite the Berry curvature in terms of charges that partially capture the effective charges and their dependencies on the nuclear velocities. With these Berry charges and charge fluctuations, we then construct our population analysis yielding atomic charges and overlap populations. Calculations at the Hartree-Fock level reveal that the atomic charges are similar to those obtained from atomic polar tensors. However, since we additionally obtain an estimate for the fluctuations of the charges and a partitioning of the atomic charges into contributions from all atoms, we conclude that the Berry population analysis is a useful alternative tool to analyze the electronic structures of molecules.

20.
Angew Chem Int Ed Engl ; 62(2): e202210494, 2023 01 09.
Article in English | MEDLINE | ID: mdl-36278811

ABSTRACT

Nanoplastics (NPs), small (<1 µm) polymer particles formed from bulk plastics, are a potential threat to human health and the environment. Orders of magnitude smaller than microplastics (MPs), they might behave differently due to their larger surface area and small size, which allows them to diffuse through organic barriers. However, detecting NPs in the environment and organic matrices has proven to be difficult, as their chemical nature is similar to these matrices. Furthermore, as their size is smaller than the (spatial) detection limit of common analytical tools, they are hard to find and quantify. We highlight different micro-spectroscopic techniques utilized for NP detection and argue that an analysis procedure should involve both particle imaging and correlative or direct chemical characterization of the same particles or samples. Finally, we highlight methods that can do both simultaneously, but with the downside that large particle numbers and statistics cannot be obtained.


Subject(s)
Plastics , Water Pollutants, Chemical , Humans , Plastics/analysis , Microplastics , Water Pollutants, Chemical/chemistry
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