External Surface Research Articles

Furfural Acetalization with Ethanol over Hierarchical vs. Conventional Beta Zeolites

AbstractA set of hierarchical Beta zeolites was synthesized using concentrated reaction mixtures and compared to conventional materials with a similar composition. The obtained zeolite catalysts were investigated in acetalization of furfural with ethanol at room temperature yielding a commercially valuable fuel additive (furfural diethyl acetal). The highest yield of the desired product (91 %) was achieved over a zeolite catalyst possessing developed mesoporosity (Vmeso 0.75 cm3/g) and a high external surface area (280 m2/g). The concentration of accessible acid sites was found to be responsible for high catalytic performance of the tested zeolitic catalysts.

Экспериментальное и численное исследование нагрева стенок камеры сгорания малоразмерного газотурбинного двигателя

The combustion chamber is one of the main components that determine the energy and mass characteristics of the propulsion system. A detailed description of the combustion chambers of some model engines running on kerosene is given. The results of fire tests and numerical studies of combustion chambers of model small-sized gas turbine engines are considered. To qualitatively compare the results of calculations with the data of a physical experiment, annealed colors are used. Based on the results of the research, a map of tem perature distribution on the walls of the combustion chamber was compiled. The internal and external surfaces of the combustion chamber are unevenly colored with tarnished colors. This coloring is a consequence of non-uniform distributions of temperature and concentration of various components of combustion products, and also indicates the formation of a spatial flow in the combustion chamber.

Experimental study on transpiration cooling through additively manufactured porous structures

Film cooling and thermal barrier coating are the most common external cooling techniques used for gas turbine components. In film cooling, coolant air is brought to the external surface via rows of discrete holes. This study investigates an alternative geometry, referred to as transpiration cooling. Here, the coolant air is brought to the external surface through an additively manufactured porous structure. An experimental study was performed to characterize the downstream cooling performance by obtaining film cooling effectiveness and heat transfer coefficient using thermochromic liquid crystals. The experimental setup was first validated using a cylindrical film cooling sample and the results were compared to results obtained from previously published film cooling studies. After validation, transpiration cooling samples were investigated. A total of three porous structure samples with different thicknesses were subjected to testing. The thickness of the porous structure had insignificant effect on both the heat transfer coefficient and the film cooling effectiveness. The samples were tested at blowing ratios ranging from 0.5 to 2.0. Results showed an increase in laterally averaged heat transfer coefficient with increasing blowing ratio and compared to cylindrical film cooling, transpiration cooling yielded significantly higher distributions. The spanwise averaged film cooling effectiveness displayed a similar trend with higher values for transpiration cooling, mainly due to a more even mixing in the lateral direction. Values of the heat flux ratio showed that the high heat transfer coefficient penalizes the porous cooling method and only for low blowing ratios may transpiration cooling be the beneficial choice. From visualizations with water and carbon dioxide, it could be concluded that the inclination angle is close to 90° which yields a chaotic flow field and, in turn, high values of the heat transfer coefficient. By changing the additive manufacturing's build direction, a more favorable inclination angle should be achievable and, thereby, an opportunity to utilize the porous structure's excellent mixing in the spanwise direction.

The Influence of the Setup on the Result of Measuring the Roundness of an Anuloid Surface

In engineering practice, anuloid surfaces are produced that are subject to strict requirements in terms of accuracy (e.g., in the bearing industry). Roundness is also often measured. The accuracy of the roundness measurement does not only depend on the accuracy of a particular metrological system. The setting of the component on the measuring device can also have a significant influence on the accuracy of the measurement. The axis of the measured surface must be perpendicular to the section in which the roundness is measured. Tilting the measured surface causes a systematic measurement error, which depends on the size of the tilt angle and the parameters of the measured surface. This study presents mathematical relations for the calculation of this error when measuring roundness on an anuloid surface. Mathematical relations for the internal and external surfaces formed by the inner and outer parts of the anuloid are derived herein. There is also a theoretical analysis of the influence of inclination and the parameters of the measured surface on the size of this error. Theoretically calculated values were compared with practically measured values of roundness. The error had a negative effect on the accuracy of the roundness measurement. It affected the roundness value, the second harmonic component, and also the roundness profile itself.

Contribution to the percolation threshold study of Silicon carbide filled polydimethylsiloxane composites used for field grading application

The correlations between the electrical behavior and microstructural properties of samples consisting of particle composites fabricated from SiC particles embedded in a silicone matrix, were investigated using X-ray computed tomography. In the voltage field range 200-1000 V/mm, the measured conductivity as a function of SiC volume fraction exhibits two distinct gaps. Upon further investigations, we attribute these observations to percolation thresholds at the microscale. The first gap, corresponding to interconnections between SiC particles that were originally disconnected, is more significant at higher voltage; while the second one, resulting from shortening conductivity pathways between the external surfaces of the samples with the increase of SiC volume fraction, seems more sensitive to lower voltages and is correlated with a decrease of the tortuosity of the percolated SiC network.

Enhancing Drug Delivery Efficacy Through Bilayer Coating of Zirconium-Based Metal-Organic Frameworks: Sustained Release and Improved Chemical Stability and Cellular Uptake for Cancer Therapy.

The development of nanoparticle (NP)-based drug carriers has presented an exciting opportunity to address challenges in oncology. Among the 100,000 available possibilities, zirconium-based metal-organic frameworks (MOFs) have emerged as promising candidates in biomedical applications. Zr-MOFs can be easily synthesized as small-size NPs compatible with intravenous injection, whereas the ease of decorating their external surfaces with functional groups allows for targeted treatment. Despite these benefits, Zr-MOFs suffer degradation and aggregation in real, in vivo conditions, whereas the loaded drugs will suffer the burst effect-i.e., the fast release of drugs in less than 48 h. To tackle these issues, we developed a simple but effective bilayer coating strategy in a generic, two-step process. In this work, bilayer-coated MOF NU-901 remained well dispersed in biologically relevant fluids such as buffers and cell growth media. Additionally, the coating enhances the long-term stability of drug-loaded MOFs in water by simultaneously preventing sustained leakage of the drug and aggregation of the MOF particles. We evaluated our materials for the encapsulation and transport of pemetrexed, the standard-of-care chemotherapy in mesothelioma. The bilayer coating allowed for a slowed release of pemetrexed over 7 days, superior to the typical 48 h release found in bare MOFs. This slow release and the related performance were studied in vitro using both A549 lung cancer and 3T mesothelioma cells. Using high-resolution microscopy, we found the successful uptake of bilayer-coated MOFs by the cells with an accumulation in the lysosomes. The pemetrex-loaded NU-901 was indeed cytotoxic to 3T and A549 cancer cells. Finally, we demonstrated the general approach by extending the coating strategy using two additional lipids and four surfactants. This research highlights how a simple yet effective bilayer coating provides new insights into the design of promising MOF-based drug delivery systems.

Performance of a rotating latent heat thermal energy storage unit with heat transfer from different surfaces

Due to the rapid growth in the demand for fast and efficient latent heat thermal energy storage system, multiple heat transfer enhancement techniques have been proposed and widely investigated. Actively or passively, rotation of the energy storage unit affects the internal natural convection and the heat transfer performance. Hence, this study is conducted to evaluate the potential of the heat transfer enhancement by rotation. A two-dimensional model with the phase change material filled in the annular space of a double tube energy storage unit is developed. The numerical simulations for the heat transfer through the internal or external surfaces of the annular space are respectively conducted. Both solidification and melting of the phase change material are taken into account by the enthalpy-porosity method. According to different heat transfer surfaces and the occurrence of solidification or melting, four arrangements are formed. It is found that the rotation of the thermal energy storage unit can reduce the solidification time as high as 46 % compared to its still counterpart, but variation of the rotation speed only produces a minor influence. The effect of rotation on the melting depends on the heat transfer direction (or surface). When the heat is transferred into the solid phase change material through the internal wall, the melting time can be gradually reduced as the rotation speed increases with a maximum of 69 %. However, when the heat is transferred through the external wall, influence of the rotation results in adverse effect. This study can guide the design of innovative high performance latent heat thermal energy storage system containing rotation unit.

DFT Analysis of the Binding of Rare Earth Nitrates at Internal and External Surfaces of MCM-22

DFT Analysis of the Binding of Rare Earth Nitrates at Internal and External Surfaces of MCM-22

Applications and technological evolution of FinFET in modern technology

FinFET technology, hailed as the successor to MOSFETs, has garnered significant attention due to its potential to address the challenges posed by the latter's scaling limitations. However, the adoption of FinFETs is not without its set of obstacles. Key issues, such as constraints imposed by material-induced bandgaps, the intricacies of manufacturing processes, and complications related to fin height, persistently challenge engineers and researchers alike. Notably, the material-induced bandgap limitations can be detrimental to the device's overall performance. The intricacies in manufacturing add layers of complexity to fabrication, making the production process not only meticulous but also expensive. Additionally, the precise control over fin height is crucial, as it has direct implications for device performance and variability. In response to these challenges, innovative solutions are continually being proposed. The advent of multiple gate designs has offered greater control over the device's electrical properties. Additionally, the integration of High-K dielectrics provides an improved gate oxide alternative, addressing the leakage current issues often observed in traditional designs. Moreover, techniques like selective epitaxial silicon growth have been introduced to rectify the external surface, ensuring better consistency and performance. Undoubtedly, these hurdles underscore the importance of relentless research and collaboration in the semiconductor industry. The drive to overcome these challenges not only pushes the boundaries of FinFET technology but also promises enhanced performance, efficiency, and scalability. This continuous evolution will undoubtedly pave the way for more refined and efficient FinFET solutions in the near future.

Disinfection of needleless connectors for catheters in one second using a hand-held UV device

The standard of care for disinfecting needleless connectors (NCs) of central venous catheters includes alcohol-containing caps or up to a 15-second scrub with alcohol or chlorhexidine. Due to the clinical impact and high cost of treating Central line-associated bloodstream infections (CLABSI), reducing the incidence of CLABSI is a priority for public health and of the Centers for Disease Control. Alcohol-containing caps have been demonstrated to disinfect external NC surfaces, but not the internal surface. Ultraviolet light (UV-C) is a strategy for disinfection of NC internal and external surfaces. Four clinically relevant bacteria (Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli,Pseudomonas aeruginosa) and Candida albicans were inoculated on NCs. Disinfection efficacy was measured after exposure to one second of 285nm UV-C light at 48mW/cm2 in a proprietary handheld device and UV-C transparent NC or standard of care. Disinfection of internal and external surfaces of NC inoculated with S aureus using alcohol caps, and UV-C was also compared. A 4-log reduction in colony forming units (CFUs) on the interior and exterior surfaces of the UV-transparent NC of clinically relevant pathogens was observed with UV-C light at this power for 1second. We demonstrated the efficacy of UV-C for the disinfection of NCs in one second using the UV-C device in benchtop studies. This device holds promise for reducing CLABSI, and clinical studies are planned.

Evaluation of Nursing Intervention Measures in Infection Control at Dialysis Units in Mosul City Hospitals

Abstract Background: Nursing staff must take adequate precautions and implement appropriate practices to substantially reduce the risk of workplace transmission of blood-borne infections to patients and staff within dialysis units. This study aimed to evaluate the intervention measures for staff nurses in the dialysis unit. Materials and Methods: A descriptive cross-sectional design was used to conduct the study from December 1, 2021, to April 1, 2022, in three Mosul City hospitals. A convenience sample was selected. Sixty nurses participated in the study. Results: The study findings show that 41.7% of the study sample was within the 25–29 year age group, and the highest percentage was of males (51.7%). Regarding qualifications, 43.3% of nurses had a bachelor’s degree, and 76.7% of them had less than 5 years of experience working in the dialysis unit. All the subjects received vaccination against the hepatitis virus. There are limitations in some nurses’ practices, such as wearing a face shield, cleaning and disinfecting the beds and chairs, and external surfaces of the machines during pre- and post-dialysis. Conclusion: The study concludes that there are clear defects in the application of some nursing procedures and measures to control the transmission of infections inside hemodialysis units in Mosul city hospitals.

Development of Ac2-26 Mesoporous Microparticle System as a Potential Therapeutic Agent for Inflammatory Bowel Diseases.

Inflammatory bowel diseases (IBDs) disrupt the intestinal epithelium, leading to severe chronic inflammation. Current therapies cause adverse effects and are expensive, invasive, and ineffective for most patients. Annexin A1 (AnxA1) is a pivotal endogenous anti-inflammatory and tissue repair protein in IBD. Nanostructured compounds loading AnxA1 or its active N-terminal mimetic peptides improve IBD symptomatology. To further explore their potential as a therapeutic candidate, the AnxA1 N-terminal mimetic peptide Ac2-26 was incorporated into SBA-15 ordered mesoporous silica and covered with EL30D-55 to deliver it by oral treatment into the inflamed gut. The systems SBA-Ac2-26 developed measurements revealed self-assembled rod-shaped particles, likely on the external surface of SBA-15, and 88% of peptide incorporation. SBA-15 carried the peptide Ac2-26 into cultured Raw 264.7 macrophages and Caco-2 epithelial cells. Moreover, oral administration of Eudragit-SBA-15-Ac2-26 (200 μg; once a day; for 4 days) reduced colitis clinical symptoms, inflammation, and improved epithelium recovery in mice under dextran-sodium sulfate-induced colitis. The absorption of SBA-15 in gut epithelial cells is typically low; however, the permeable inflamed barrier can enable microparticles to cross, being phagocyted by macrophages. These findings suggest that Ac2-26 is successfully delivered and binds to its receptors in both epithelial and immune cells, aligning with the clinical results. Our findings demonstrate a simple and cost-effective approach to delivering Ac2-26 orally into the inflamed gut, highlighting its potential as non-invasive IBD therapy.

Portable and highly enhanced surface enhanced Raman scattering and photocatalytic activity of cost-effective hierarchical hollow metal organic frameworks heterostructures induced by etched titanium sheet

In order to effectively detect and remove organic toxics in wastewater, the facile construction of plug and play bifunctional materials is very vital. Herein, a kind of metal-organic frameworks (MIL-53 (Fe) with hollow tubular structure was induced by an etched Ti sheet (ET), and then small sized Ag nanoparticles (Ag NPs) were in-situ anchored evenly on the internal and external surfaces of MIL-53 (Fe). Subsequently, a new type of bifunctional material (ETMA) was assembled. Surface enhanced Raman scattering (SERS) and photocatalytic activity of the material were investigated with crystal violet (CV, a carcinogenic and teratogenic toxic) as an analyte. The results found that trace amount of CV (1 × 10−12 M) can still be sensitively detected by the fabricated ETMA, and analysis enhancement factors as high as 6.9 × 105 even though only 1.39 wt % Ag was contained in the ETMA. Moreover, nearly 100 % of CV can be rapidly degraded by the ETMA after irradiated for 15 min, which was 44.47 times and 7.27 times faster than those of ET-Ag (ETA) and ET-MIL-53 (Fe) (ETM), respectively. Additionally, the removal efficiency of total organic carbon (TOC) was as high as 75.44 %. The remarkable enrichment effect, the strong interaction among components, and the synergistic effect in the target ETMA material were responsible to the dramatically enhanced SERS and photocatalytic performances. In addition, the cost-effective ETMA exhibited excellent uniformity, repeatability, stability, and recyclability towards the detection and removal of CV in actual water samples, showing great potentials in monitoring and removing organic pollutants in practical ecological environment.

Montmorillonite-Silica-Graphene oxide composite incorporating with chiral thiourea for the Strecker reaction

The present study has successfully intercalated graphene oxide (GO) nanosheets and silica into the montmorillonite (MMT) interlayer and deposited them onto its external surface to make montmorillonite, silica, and graphene oxide composite (MMT-silica-GO). The as-prepared composite demonstrates improved thermal stability compared to neat MMT and GO. It was followed by incorporating chiral thiourea (CTU) scaffold into MMT-silica-GO-based composite to establish chiral MMT-silica-GO-CTU-based heterogeneous system and tested over Strecker reaction, revealing high activity and selectivity. FTIR, Raman spectroscopy, powder X-ray diffraction, SAXS, XPS, BET, SEM, EDAX, and thermogravimetric analysis were used to characterize the samples. It was credited to the synergistic effect between the composite components that enhanced access to active sites and dispersion of catalyst. Across the board, the chiral MMT-silica-GO-CTU-based heterogeneous system appears to be a promising candidate for the Strecker reaction.

Modulated Self-Assembly of Catalytically Active Metal-Organic Nanosheets Containing Zr6 Clusters and Dicarboxylate Ligands.

Two-dimensional metal-organic nanosheets (MONs) have emerged as attractive alternatives to their three-dimensional metal-organic framework (MOF) counterparts for heterogeneous catalysis due to their greater external surface areas and higher accessibility of catalytically active sites. Zr MONs are particularly prized because of their chemical stability and high Lewis and Brønsted acidities of the Zr clusters. Herein, we show that careful control over modulated self-assembly and exfoliation conditions allows the isolation of the first example of a two-dimensional nanosheet wherein Zr6 clusters are linked by dicarboxylate ligands. The hxl topology MOF, termed GUF-14 (GUF = Glasgow University Framework), can be exfoliated into monolayer thickness hns topology MONs, and acid-induced removal of capping modulator units yields MONs with enhanced catalytic activity toward the formation of imines and the hydrolysis of an organophosphate nerve agent mimic. The discovery of GUF-14 serves as a valuable example of the undiscovered MOF/MON structural diversity extant in established metal-ligand systems that can be accessed by harnessing the power of modulated self-assembly protocols.

Boosting the efficient combustion of plastic wastes via tailoring the oxygen vacancies of Ce-Zr solid solution

Novel-design catalyst is a promising candidate for the clean combustion of plastic wastes, alleviating the environmental and energy crisis. Herein, Ce-Zr catalysts with different oxygen vacancies were prepared by tailoring the Zr-content to optimize the catalytic performance in plastic wastes combustion. The detailed characterization results confirmed that Zr has been successfully incorporated into CeO2 lattice, which decreased the crystal size and increased the surface area. Moreover, the Zr-doping caused the lattice distortion, i.e., Ce-O around the doped Zr was elongated to compensate the shortness of Zr-O, which made it easy to break and generate oxygen vacancies. DFT calculation results revealed that Ce0.8Zr0.2O2 exhibited a lower energy of oxygen vacancies formation (2.22 eV) and O2 adsorption (−1.20 eV) than that of CeO2 (2.46 eV and −0.42 eV). It indicated that the Zr-doping improved the oxygen vacancies and O2 adsorption of Ce-Zr catalysts. Ce0.8Zr0.2O2 significantly improved plastic wastes combustion at 250 °C, and achieved a conversion of 14.3 %, 21.8 %, 100 %, 22.4 % and 13.7 % for high-density polyethylene, low-density polyethylene, polypropylene, polystyrene and real plastic wastes, which was 2–3 times that of the non-catalytic combustion. This has been attributed to the superiority of Ce0.8Zr0.2O2 in the crystal and texture structure as well as the oxygen vacancies and O2 adsorption, i.e., the improved external surface enhanced the contact with polymer molecules, and the improved oxygen vacancies as well as O2 adsorption provided more active oxygen.

Antibiotic-associated microbiotoxicity and possible ways of its prevention. Review

In recent years, there has been an exponential increase in interest to the human microbiome, a community of living microorganisms that colonize all external and internal surfaces of the body together with their microbial metabolites, organic compounds, and genetic material. Gut microbes are involved in a wide range of physiological functions, including the production of essential vitamins, bile salts, and short‑chain fatty acids such as butyrate; they inhibit tumor formation and inflammation, regulate glucose, lipid and energy exchanges; regulate adaptive immunity; play a central role in the development of immune tolerance to microbial and non‑microbial antigens and maintenance of the integrity of protective barriers. Resident microbes are important in the production of neurotransmitters including dopamine, serotonin and γ‑aminobutyric acid, as well as hormones such as glucagon‑like peptide 1 and a complex network of neurological, endocrine and microbial components involved in the homeostasis of the gut–microbiota–brain axis. Numerous studies have established the association between antimicrobial use, microbiome damage, and adverse health outcomes. Recently, by analogy with nephrotoxicity or hepatotoxicity, a new term «microbiotoxicity» has been proposed, which encompasses the unwanted side effects of antibiotics on the patient’s microbiome. It is emphasized that clinicians must carefully weigh the benefits of antibiotics in the treatment of infections against their microbiotoxic effects when making individual decisions about prescribing antibiotic therapy. An exception to this is rifaximin, with its atypical antimicrobial effects it is able to induce positive modulation of intestinal microflora, creating a favorable environment for the growth of bacteria useful for the host organism without changing their general composition. The review gives analysis of the role of the microbiome as a complex immunological, endocrine, and neurological ecosystem and the potentially harmful consequences of antibiotic exposure to it.

Effectiveness of trancutaneous electrical nerve stimulationon improving hyposalivation in xerostomia patients with diabetes mellitus

The aim of the study is to analyse the effectiveness of TENS [transcutaneous electrical nerve stimulation] on improving hyposalivation in Xerostomia patients with diabetes mellitus. This was an experimental study with pre and post-test type. Sixty (60) Diabetes mellitus patients with hyposalivation condition were treated with TENS on their external surface of salivary glands and other corresponding buccal nerves. The duration of the treatment is for 15-20 minutes 1 session per day four sessions a week for 4 weeks. A simplified questionnaire is used as a screening tool and Sialometry method is used to analyze the saliva secretion. Saliva samples were collected from the subjects prior to TENS stimulation. The present study states that, the salivary secretion was increased after TENS application in continuous mode (p<0.001) and burst mode (p<0.001). It was illustrated when compared to saliva taken before therapy, particularly in xerostomic diabetes mellitus patients. Bangladesh J. Sci. Ind. Res. 59(1), 01-06, 2024

Catalytic pyrolysis of high-density polyethylene (HDPE) over hierarchical ZSM-5 zeolites produced by microwave-assisted chelation-alkaline treatment

A new microwave (MW) assisted chelation-alkaline strategy was developed to produce hierarchical ZSM-5 zeolites (with external surface area of 203 m2/g) in minutes, leading to the formation of heterogeneous structure with a high-silica shell and aluminium-rich core (silicon-to-aluminium ratios of 49.2 and 37.6, respectively). The zeolites were assessed comparatively by catalytic pyrolysis of high-density polyethylene (HDPE). Compared to the mesoporous ZSM-5 zeolite prepared by the conventional alkaline treatment (via desilication by the NaOH aqueous solution), the hierarchical zeolite by the MW-assisted method showed comparable kinetics in catalytic pyrolysis of HDPE, but with the improved stability in the cyclic pyrolysis-regeneration tests. The improved stability could be due to the better-preserved structural integrity thanks to the relatively milder surface etching by the MW-assisted chelation dealumination method. In addition, compared to the parent ZSM-5, the product distribution of HDPE catalytic pyrolysis over the hierarchical ZSM-5 zeolite showed a higher portion of oil products (i.e., 12 wt% vs. 6.9 wt%) and an improved alkane-to-olefin ratio in the oil products (2.22 vs. 1.86, respectively) due to the reduced acidity and improved hydrogen transfer ability. The MW-assisted chelation-alkaline treatment could be a new strategy to regulate the trade-off between stability and activity of zeolites for catalytic applications.

Natural external plastron mold of the Triassic turtle Proterochersis: An unusual mode of preservation.

Impressions of vertebrate bodies or their parts, such as trace fossils and natural molds of bones, are a valuable source of information about ancient faunas which may supplement the standard fossil record based on skeletal elements. Whereas trace fossils of animal activity are relatively common and actively studied within the field of ichnology, and natural impressions of internal or external surfaces are a frequent preservation mode in fossil invertebrates, natural molds of bones are comparatively rare and less extensively documented and discussed. Among them, internal molds (steinkerns) of turtle shells are a relatively well-known form of preservation, but the mechanisms and taphonomic prerequisites leading to their formation are poorly studied. External shell molds are even less represented in the literature. Herein, we describe a historic specimen of a natural external turtle plastron mold from the Triassic (Norian) Löwenstein Formation of Germany-a formation which also yielded a number of turtle steinkerns. The specimen is significant not only because it represents an unusual form of preservation, but also due to its remarkably large size and the presence of a potential shell pathology. Although it was initially interpreted as Proterochersis sp., the recent progress in the knowledge of proterochersid turtles leading to an increase in the number of known taxa within that group allows us to verify that assessment. We confirm that the specimen is morphologically consistent with the genus and tentatively identify it as Proterochersis robusta, the only representative of that genus from the Löwenstein Formation. We note, however, that its size exceeds the size observed thus far in Proterochersis robusta and fits within the range of Proterochersis porebensis from the Grabowa Formation of Poland. The marks interpreted as shell pathology are morphologically consistent with Karethraichnus lakkos-an ichnotaxon interpreted as a trace of ectoparasites, such as leeches. This may support the previously proposed interpretation of Proterochersis spp. as a semiaquatic turtle. Moreover, if the identification is correct, the specimen may represent a very rare case of a negative preservation of a named ichnotaxon. Finally, we discuss the taphonomy of the Löwenstein Formation turtles in comparison with other Triassic turtle-yielding formations which show no potential for the preservation of internal or external shell molds and propose a taphonomic model for the formation of such fossils.