Retrograde intramedullary nail fixation with oblique fixed angle screws versus locking plates in periprosthetic supracondylar fractures after total knee arthroplasty.

PURPOSE: Common surgical procedures in the treatment of periprosthetic distal femur fractures (PPFF) include osteosynthesis with fixed angle locking plates (LP) and retrograde intramedullary nails (RIN). This study aimed to compare LPs to RINs with oblique fixed angle screws in terms of complications, radiographic results and functional outcome. METHODS: 63 PPFF in 59 patients who underwent treatment in between 2009 and 2020 were included and retrospectively reviewed. The anatomic lateral and posterior distal femoral angle (aLDFA and aPDFA) were measured on post-surgery radiographs. The Fracture Mobility Score (FMS) pre- and post-surgery, information about perceived instability in the operated leg and the level of pain were obtained via a questionnaire and previous follow-up (FU) examinations in 30 patients (32 fractures). RESULTS: The collective (median age: 78 years) included 22 fractures treated with a RIN and 41 fractures fixed with a LP. There was no difference in the occurrence of complications (median FU: 21.5 months) however the rate of implant failures requiring an implant replacement was higher in fractures treated with a LP (p = 0.043). The aPDFA was greater in fractures treated with a RIN (p = 0.04). The functional outcome was comparable between both groups (median FU: 24.5 months) with a lower outcome in the post-surgery FMS (p = < 0.001). CONCLUSION: Fractures treated with RIN resulted in an increased recurvation of the femur however the rate of complications and the functional outcome were comparable between the groups. The need for implant replacements following complications was higher in the LP group.

Biomechanical testing of different fixation techniques for intraoperative proximal femur fractures: a technical note.

Intraoperative proximal femoral fractures (IPFF) represent a rare but challenging complication of total hip arthroplasties. They usually occur as a longitudinal split. This pilot trial aimed to compare the biomechanical primary stability of different fixation techniques for IPFF. Standardised longitudinal medial split fractures of the proximal femur (type II, Modified Mallory Classification) were created in artificial osteoporotic and non-osteoporotic composite femora after implantation of a cementless femoral stem. Five different fixation techniques were compared: cerclage band, cerclage wiring with one or two wires, and lag screw fixation with one or two lag screws. A quasi-static loading protocol was applied and failure loads were evaluated. The observed median failure loads were 4192N (3982N - 5189N) for one cerclage band, 4450N (3577N - 4927N) for one cerclage wire, 5016N (4175N - 5685N) for two cerclage wires, 6085N (5000N - 8907N) for one lag screw, and 4774N (4509N - 8502N) for two lag screws. Due to the wide range of failure loads within the experimental groups, there were no observable differences between the groups. All fixation techniques provided sufficient primary stability in osteoporotic and non-osteoporotic composite bones. Further cadaveric studies with larger sample sizes may be needed to confirm the results presented here.

Leveraging Dynamic Heterogeneous Networks to Study Transnational Issue Publics. The Case of the European COVID-19 Discourse on Twitter.

The ongoing COVID-19 pandemic constitutes a critical phase for the transnationalization of public spheres. Against this backdrop, we ask how transnational COVID-19 related online discourse has been throughout the EU over the first year of the pandemic. Which events triggered higher transnational coherence or national structuration of this specific issue public on Twitter? In order to study these questions, we rely on Twitter data obtained from the TBCOV database, i.e., a dataset for multilingual, geolocated COVID-19 related Twitter communication. We selected corpora for the 27 member states of the EU plus the United Kingdom. We defined three research periods representing different phases of the pandemic, namely April (1st wave), August (interim) and December 2020 (2nd wave) resulting in a set of 51,893,966 unique tweets for comparative analysis. In order to measure the level and temporal variation of transnational discursive linkages, we conducted a spatiotemporal network analysis of so-called Heterogeneous Information Networks (HINs). HINs allow for the integration of multiple, heterogeneous network entities (hashtags, retweets, @-mentions, URLs and named entities) to better represent the complex discursive structures reflected in social media communication. Therefrom, we obtained an aggregate measure of transnational linkages on a daily base by relating these linkages back to their geolocated authors. We find that the share of transnational discursive linkages increased over the course of the pandemic, indicating effects of adaptation and learning. However, stringent political measures of crisis management at the domestic level (such as lockdown decisions) caused stronger national structuration of COVID-19 related Twitter discourse.

The EPINetz Twitter Politicians Dataset 2021. A New Resource for the Study of the German Twittersphere and Its Application for the 2021 Federal Elections.

This research note introduces the EPINetz Twitter Politicians Dataset, a comprehensive dataset of 2449 Twitter accounts of German parliamentarians, minsters, state secretaries, parties, and ministries on a state, federal, and European Union level for the year 2021. This hand-curated dataset not only provides up-to-date information on elected officials, but it also includes additional variables such as their party affiliation, age, and gender. Furthermore, it provides linkages to additional data sources by providing the accounts' Wikidata and Abgeordnetenwatch (Parliamentwatch) IDs. While it does not provide actual tweet data, the dataset will be a valuable resource for researchers by providing easy access to elected German politicians. We demonstrate some of the dataset's uses with an analysis of the 2021 German Federal Elections. The full dataset can be accessed via 10.7802/2415. Supplementary Information: The online version of this article (10.1007/s11615-022-00405-7) contains supplementary material, which is available to authorized users.

Orbital cellulitis secondary to sinusitis in upstate New York: current incidence, seasonality, severity, management and outcomes.

PURPOSE: While sinusitis carries a seasonal variation, the temporal features of sinusitis-related orbital cellulitis (SRC) are unclear. This study analyzes the incidence, seasonality, management, and outcomes of SRC in northeastern New York. METHODS: A retrospective review of 79 patients was performed from January 2008 - December 2018. Cases of orbital cellulitis without comitant sinusitis were excluded. Demographic, radiographic, clinical features, month at presentation, interventions (surgical and nonsurgical), microbiology, and hospitalization duration were recorded. Fisher-exact test, Mann-Whitney test, and Kruskal Wallis test statistical analyses were performed in consultation with our institution's statistician via a dedicated software package (vassarstats.net). RESULTS: 79 patients were admitted for SRC. 25 patients were treated with antibiotics only, 31 underwent orbitotomy exclusively and 23 received combined orbitotomy and functional endoscopic sinus surgery (FESS). Of the 31 patients who underwent orbitotomy only, 8 (26%) returned to the operating room. In contrast, of those who underwent concomitant orbitotomy and FESS, only one patient (4.3%) required re-operation (fisher exact test, p = .021). The median length of stay for the antibiotic-only group (4 days), orbitotomy-only group (6 days), and combined surgery group (5 days) were statistically different (Kruskal Wallis, p = .004, Figure 3). Interestingly, there was no significant relationship of incidence or severity of SRC related to seasonality (fisher-exact test, p = .76). CONCLUSION: Our findings suggest that cases requiring surgical management for SRC should undergo coinitial orbitotomy with FESS to reduce re-operation rates. Additionally, SRC incidence and severity did not correlate with season.

Risk factors for intraoperative greater trochanteric fractures in hemiarthroplasty for intracapsular femoral neck fractures.

PURPOSE: Hemiarthroplasty is widely accepted as the treatment of choice in elderly patients with a displaced intracapsular femoral neck fracture. Intraoperative greater trochanteric fractures thwart this successful procedure, resulting in prolonged recovery, inferior outcome, and increased risk of revision surgery. Hence, this study analyzed factors potentially associated with an increased risk for intraoperative greater trochanteric fracture. METHODS: This retrospective study included 512 hemiarthroplasties in 496 patients with a geriatric intracapsular femoral neck fracture from July 2010 to March 2020. All patients received the same implant type of which 90.4% were cemented and 9.6% non-cemented. Intra- and postoperative radiographs and reports were reviewed and particularly screened for greater trochanteric fractures. RESULTS: Female patients accounted for 74% and mean age of the patients was 82.3 (± 8.7) years. 34 (6.6%) intraoperative greater trochanteric fractures were identified. In relation to patient-specific factors, only a shorter prothrombin time was found to be significantly associated with increased risk of intraoperative greater trochanteric fracture (median 96%, IQR 82-106% vs. median 86.5%, IQR 68.8-101.5%; p = 0.046). Other factors associated with greater trochanteric fracture were a shorter preoperative waiting time and changes in perioperative settings. Outcome of patients with greater trochanteric fracture was worse with significantly more surgical site infection requiring revision surgery (17.6% vs. 4.2%, p = 0.005). CONCLUSION: Prolonged prothrombin time, a shorter preoperative waiting time, and implementing new procedural standards and surgeons may be associated with an increased risk of a greater trochanteric fracture. Addressing these risk factors may reduce early periprosthetic infection which is strongly related to greater trochanteric fractures.

Sterically constrained tricyclic phosphine: redox behaviour, reductive and oxidative cleavage of P-C bonds, generation of a dilithium phosphaindole as a promising synthon in phosphine chemistry.

The redox behaviour of sterically constrained tricyclic phosphine 3a was investigated by spectroelectrochemistry. The data suggested a highly negative reduction potential with the reversible formation of a dianionic species. Accordingly, 3a reacted with two equivalents of Li/naphthalene by reductive cleavage of a P-C bond of one of the PC4 heterocycles. The resulting dilithium compound 5 represents a phosphaindole derivative with annulated aromatic C6 and PC4 rings. It is an interesting starting material for the synthesis of new heterocyclic molecules, as was shown by treatment with Me2SiCl2 and PhPCl2. The structures of the products (6 and 7) formally reflect ring expansion by insertion of silylen or phosphinidene fragments into a P-C bond of 3a. Treatment of 3a with H2O2 did not result in the usually observed transfer of a single O atom to phosphorus, but oxidative cleavage of a strained PC4 ring afforded a bicyclic phosphinic acid, R2PO2H.

Metaphyseal sleeves in arthroplasty of the knee : A suitable tool in management of major metaphyseal bone loss.

BACKGROUND: This study examined the clinical outcome following revision arthroplasty of the knee joint and severe arthrosis with metaphyseal bone defects and instability using metaphyseal sleeves. We analyzed the results based on established scores and recorded the complications occurring on revision arthroplasty. MATERIAL AND METHODS: Patients with revision arthroplasty of the knee and metaphyseal bone defects grade III according to the Anderson Orthopedic Research Institute (AORI) classification were included (16 patients, 9 females and 7 males). In all cases, surgery was performed using an endoprosthesis COMPLETE™ revision knee system with metaphyseal sleeves. RESULTS: All patients had a significant reduction in pain level after revision surgery. The median HSS score in the cohort with primary arthroplasty was 84 and in the cohort with revision arthroplasty 73 and the KSS was 83 and 55, respectively. According to the HSS an excellent result was achieved by 50% of the patients in the primary arthroplasty group and 25% in the revision group. Only three patients were considered to have an insufficient result. Postoperative pain was significantly reduced in both groups. The median ROM was 112° flexion in the primary arthroplasty group and 95° in the revision group. An extension deficit was observed in three patients and four patients showed prolonged wound healing postoperatively (25%), which was treated conservatively and did not lead to septic changes. CONCLUSION: The use of metaphyseal sleeves in patients with bone defects is a suitable instrument with no negative impact on the outcome both in primary and revision arthroplasty. Further studies with larger study groups and analysis of long-term results after use of such endoprosthetic components should be conducted.

Stabilization of a Clayey Soil with Ladle Metallurgy Furnace Slag Fines.

The research study described in this paper investigated the potential to use steel furnace slag (SFS) as a stabilizing additive for clayey soils. Even though SFS has limited applications in civil engineering infrastructure due to the formation of deleterious expansion in the presence of water, the free CaO and free MgO contents allow for the SFS to be a potentially suitable candidate for clayey soil stabilization and improvement. In this investigation, a kaolinite clay was stabilized with 10% and 15% ladle metallurgy furnace (LMF) slag fines by weight. This experimental study also included testing of the SFS mixtures with the activator calcium chloride (CaCl2), which was hypothesized to accelerate the hydration of the dicalcium silicate phase in the SFS, but the results show that the addition of CaCl2 was not found to be effective. Relative to the unmodified clay, the unconfined compressive strength increased by 67% and 91% when 10% and 15% LMF slag were utilized, respectively. Likewise, the dynamic modulus increased by 212% and 221% by adding 10% and 15% LMF slag, respectively. Specifically, the LMF slag fines are posited to primarily contribute to a mechanical rather than chemical stabilization mechanism. Overall, these findings suggest the effective utilization of SFS as a soil stabilization admixture to overcome problems associated with dispersive soils, but further research is required.

Improved field-portable system to measure Cs-137 in wildlife.

We have developed an improved system to measure Cs-137 in wildlife at the Savannah River Site. This field-portable system consists of a shielded 5 cm by 10 cm by 40 cm NaI detector controlled by an Ametek Ortec Digibase. Measurement of an animal's radioactivity is made by placing the animal at a predefined location on the detector system for a one minute count-time. The counts, animal type, and animal weight are then used as inputs to an algorithm which calculates the amount of Cs-137 within the whole animal and within the edible meat portion of the animal. The results from these calculations are used to estimate the received dose from eating this animal and is included in the Savannah River Site's Hunter Dose Tracking System. This system has a detection limit of 0.60 pCi/g (22.20 Bq/kg) with a typical measurement uncertainty of less than 0.32 pCi/g (11.84 Bq/kg).

Tridentate Ligand with Three Carbanions as Donor Atoms: Formation of Dinuclear, Heptacyclic Complexes of Boron, Aluminum, or Gallium with B-C-B, Al-C-Al, or Ga-C-Ga Three-Center-Two-Electron Bonds.

The trilithium compound 1,3-[PhMe2Si-C(Li)═C(H)]2C6H3Li (2b) reacted with BCl3, AlCl3, or GaCl3 by salt elimination to yield dinuclear heptacyclic compounds (4). Two tridentate tricarbanionic ligands coordinate two B, Al, or Ga atoms and adopt a helical arrangement of the ligands around a central E2 unit. The unusual structures comprise E2C2 heterocycles with two 3c-2e (three-center-two-electron) E-C-E bonds and two C atoms of aromatic rings in the bridging positions. While such a bonding situation is well-documented in Al chemistry, it is rare for B and Ga compounds. Insight into the bonding situation of the molecules is provided by DFT calculations.

Sterically Constrained Bicyclic Phosphines: A Class of Fascinating Compounds Suitable for Application in Small Molecule Activation and Coordination Chemistry.

Bicyclic phosphines with two annulated, electronically unsaturated five-membered heterocycles are available through facile routes. In most cases, their phosphorus atoms are bound to heteroatoms such as oxygen or nitrogen (PN3 or PN2 O), whereas homoleptic coordination by three sp2 -hybridized carbon atoms has been reported only recently. Steric strain causes unique reactivity. Oxidative addition of halogens, N-H or O-H bonds have afforded phosphoranes as valuable materials for secondary processes. Ring opening was identified as an important step for the understanding of these reactions and has been observed experimentally with a diphosphorus-based ring system. A PH2 derivative has been considered as a model system for small molecule activation, and hydrogen transfer to a diazo compound was observed experimentally. Several of these phosphines are excellent ligands for the coordination of transition-metal atoms. The very bulky PC3 compound has a basicity similar to that of PPh3 and may allow the synthesis of complexes with unusually low coordination numbers at the metal atoms. These phosphines found recently renewed interest as promising reagents in various secondary transformations such as the activation of σ-bonds or in coordination chemistry.

Risk factors for early infection following hemiarthroplasty in elderly patients with a femoral neck fracture.

PURPOSE: Periprosthetic joint infections (PJI) after hemiarthroplasty for geriatric femoral neck fractures are a devastating complication that results in serious morbidity and increased mortality. Identifying risk factors associated with early infection after HA for hip fractures may offer an opportunity to address and prevent this complication in many patients. The aim of this study was to evaluate preoperative risk factors for early PJI after HA in hip fracture patients. METHODS: From January 2010 to December 2015, 312 femoral neck fractures (AO/OTA 31-B) in 305 patients were included in this single-center, retrospective study. PJI was defined according to the Centers for Disease Control (CDC) definition of deep incisional surgical site infection. Early infection referred to a postoperative period of 4 weeks. Binary univariable and multivariable regression analysis with backward elimination was applied to identify predictors of PJI. RESULTS: Median age of all patients was 83.0 (IQR 76-89) years. We identified 16 (5.1%) early PJI which all required surgical revision. Median length of in-hospital stay (LOS) was 20.0 (IQR 10-36) days after PJI compared to 10.0 (8-15) days without deep wound infection. In-hospital mortality was 30.8 vs. 6.6%, respectively. Preoperative CRP levels (OR 1.009; 95% CI 1.002-1.018; p = 0.044), higher BMI (OR 1.092; 95% CI 1.002-1.189; p = 0.044) and prolonged surgery time (OR 1.013; 95% CI 1.000-1.025; p = 0.041) were independent risk factors for PJI. Excluding infection following major revision due to mechanical complications identified preoperative CRP levels (OR 1.012; 95% CI 1.003-1.021; p = 0.007) and chronic glucocorticoid therapy (OR 6.314; 95% CI 1.223-32.587; p = 0.028) as risk factors, a clear trend was seen for higher BMI (OR 1.114; 95% CI 1.000-1.242; p = 0.051). A cut-off value at CRP levels ≥ 14 mg/l demonstrated a sensitivity of 69% and a specificity of 70% with a fair accuracy (AUC 0.707). CONCLUSION: Preoperative serum CRP levels, higher BMI and prolonged surgery time are independent predictors of early PJI. Excluding PJI secondary to major revision surgery revealed chronic glucocorticoid use as a risk factor apart from preoperative CRP levels.

Femoral neck fractures in old age treated with hemiarthroplasty : Effects of preoperative waiting time and timing of surgery on the risk of periprosthetic infections.

BACKGROUND: Hemiarthroplasty is an established treatment for femoral neck fractures (FNF) in old age; however, approximately 20-30% of patients die within 1 year after surgery. Periprosthetic joint infections (PJI) are one of the severest complications and associated with a high mortality rate. In this retrospective study of aged patients with FNF treated with hemiarthroplasty, the incidence of PJI was evaluated with respect to the influence of the delay to and timing of surgical treatment. PATIENTS AND METHODS: The data of patients suffering from FNF and admitted to this hospital between January 2012 and December 2014 were evaluated. Demographic data, timing of surgery, intraoperative complications, PJI and other general complications, hospitalization time and mortality were recorded. RESULTS: In this study 178 patients were included in the follow-up (114 women and 64 men). The median age of the patients was 83 years (range 55-105 years). The rate of PJI was 3.9% (7/178) and mortality was 5.6% (10/178). Patients with PJI after hemiarthroplasty had a significantly longer hospital stay (17 vs. 10 days, p < 0.001) and a higher mortality (28% vs. 4.7%). No significant differences were found between the groups with respect to the time from admission to surgery. CONCLUSION: The occurrence of PJI after hip joint fractures treated with hemiarthroplasty in aged patients is associated with a significant increase in mortality. Risk factors include a longer surgery time, diabetes, intraoperative complications, postoperative bleeding and wound healing disorders. Surgical treatment within the first 24 h should be aimed for but not at the expense of adequate patient preparation or neglecting the patient's individual risk factors.

A Sterically Constrained Tricyclic PC3 Phosphine: Coordination Behavior and Insertion of Chalcogen Atoms into P-C Bonds.

A tricyclic phosphine has been generated that has a rigid molecular backbone with the P atoms exclusively bound to C(sp2 ) atoms as well as a very large Tolman angle and buried volume. It is an interesting new ligand in coordination chemistry (Au, Pd complexes) and shows unusual insertion reactions into its endocyclic P-C bonds facilitated by its inherent molecular strain.

A new classification of TKA periprosthetic femur fractures considering the implant type.

BACKGROUND: The treatment aims of periprosthetic fractures (PPF) of the distal femur are a gentle stabilization, an early load-bearing capacity and a rapid postoperative mobilization of the affected patients. For the therapy planning of PPF a standardized classification is necessary which leads to a clear and safe therapy recommendation. Despite different established classifications, there is none that includes the types of prosthesis used in the assessment. For this purpose, the objective of this work is to create a new more extensive fracture and implant-related classification of periprosthetic fractures of the distal femur based on available classifications which allows distinct therapeutic recommendations. METHODS: In a retrospective analysis all patients who were treated in the University Hospital Leipzig from 2010 to 2016 due to a distal femur fracture with total knee arthroplasty (TKA) were established. To create an implant-associated classification the cases were discussed in a panel of experienced orthopaedists and well-practiced traumatologists with a great knowledge in the field of endoprosthetics and fracture care. In this context, two experienced surgeons classified 55 consecutive fractures according to Su et al., Lewis and Rorabeck and by the new created classification. In this regard, the interobserver reliability was determined for two independent raters in terms of Cohen Kappa. RESULTS: On the basis of the most widely recognized classifications of Su et al. as well as Lewis and Rorabeck, we established an implant-dependent classification for PPF of the distal femur. In accordance with the two stated classifications four fracture types were created and defined. Moreover, the four most frequent prosthesis types were integrated. Finally, a new classification with 16 subtypes was generated based on four types of fracture and four types of prosthesis. Considering all cases the presented implant-associated classification (κ = 0.74) showed a considerably higher interobserver reliability compared to the other classifications of Su et al. (κ = 0.39) as well as Lewis and Rorabeck (κ = 0.31). Excluding the cases which were only assessable by the new classification, it still shows a higher interobserver reliability (κ = 0.70) than the other ones (κ = 0.63 or κ = 0.45). CONCLUSIONS: The new classification system for PPF of the distal femur following TKA considers fracture location and implant type. It is easy to use, shows agood interobserver reliability and allows conclusions to be drawn on treatment recommendations. Moreover, further studies on the evaluation of the classification are necessary and planned.

Calcite dissolution rate spectra measured by in situ digital holographic microscopy.

Digital holographic microscopy in reflection mode is used to track in situ, real-time nanoscale topography evolution of cleaved (104) calcite surfaces exposed to flowing or static deionized water. The method captures full-field holograms of the surface at frame rates of up to 12.5 s-1. Numerical reconstruction provides 3D surface topography with vertical resolution of a few nanometers and enables measurement of time-dependent local dissolution fluxes. A statistical distribution, or spectrum, of dissolution rates is generated by sampling multiple area domains on multiple crystals. The data show, as has been demonstrated by Fischer et al. (2012), that dissolution is most fully described by a rate spectrum, although the modal dissolution rate agrees well with published mean dissolution rates (e.g., 0.1 µmol m-2 s-1 to 0.3 µmol m-2 s-1). Rhombohedral etch pits and other morphological features resulting from rapid local dissolution appear at different times and are heterogeneously distributed across the surface and through the depth. This makes the distribution in rates measured on a single crystal dependent both on the sample observation field size and on time, even at nominally constant undersaturation. Statistical analysis of the inherent noise in the DHM measurements indicates that the technique is robust and that it likely can be applied to quantify and interpret rate spectra for the dissolution or growth of other minerals.

Dissolution Kinetics of Cubic Tricalcium Aluminate Measured by Digital Holographic Microscopy.

In situ digital holographic microscopy is used to characterize the dissolution flux of polycrystalline cubic tricalcium aluminate (C3A-c). The surface dissolves at rates that vary considerably with time and spatial location. This implies a statistical distribution of fluxes, but an approximately steady-state median rate was obtained by using flowing solutions and by reducing the water activity in the solution. The dissolution flux from highly crystalline C3A-c depends on the water activity raised to an empirically derived exponent of 5.2 and extrapolates to a median flux of - 2.1 µmol m-2 s-1 in pure water with an interquartile range of 3.2 µmol m-2 s-1. The flux from a less crystalline source of C3A-c has an empirical water activity exponent of 4.6 and an extrapolated median flux of only -1.4 µmol m-2 s-1 in pure water with an interquartile range of 1.9 µmol m-2 s-1. These data suggest that the bulk dissolution rate of C3A-c can vary by at least 30% from one source to another and that variability in the local rate within a single material is even greater because of the heterogeneous spatial distribution of structural characteristics (i.e., degree of crystallinity, chemical impurities, and defects).

In situ nanoscale observations of gypsum dissolution by digital holographic microscopy.

Recent topography measurements of gypsum dissolution have not reported the absolute dissolution rates, but instead focus on the rates of formation and growth of etch pits. In this study, the in situ absolute retreat rates of gypsum (010) cleavage surfaces at etch pits, at cleavage steps, and at apparently defect-free portions of the surface are measured in flowing water by reflection digital holographic microscopy. Observations made on randomly sampled fields of view on seven different cleavage surfaces reveal a range of local dissolution rates, the local rate being determined by the topographical features at which material is removed. Four characteristic types of topographical activity are observed: 1) smooth regions, free of etch pits or other noticeable defects, where dissolution rates are relatively low; 2) shallow, wide etch pits bounded by faceted walls which grow gradually at rates somewhat greater than in smooth regions; 3) narrow, deep etch pits which form and grow throughout the observation period at rates that exceed those at the shallow etch pits; and 4) relatively few, submicrometer cleavage steps which move in a wave-like manner and yield local dissolution fluxes that are about five times greater than at etch pits. Molar dissolution rates at all topographical features except submicrometer steps can be aggregated into a continuous, mildly bimodal distribution with a mean of 3.0 µmolm-2 s-1 and a standard deviation of 0.7 µmolm-2 s-1.

Phase Uncertainty in Digital Holographic Microscopy Measurements in the Presence of Solution Flow Conditions.

Digital holographic microscopy (DHM) is a surface topography measurement technique with reported sub-nanometer vertical resolution. Although it has been made commercially available recently, few studies have evaluated the uncertainty or noise in the phase measurement by the DHM. As current research is using the DHM to monitor surface topography changes of dissolving materials under flowing water conditions, it is necessary to evaluate the effect of water and flow rate on the uncertainty in the measurement. Uncertainty in this study was concerned with the temporal standard deviation per pixel of the reconstructed phase. Considering the effects of solution flow rate, magnification, objective lens type (air or immersion), and experimental configuration, measurements under static conditions in air and in water with an immersion lens yielded the smallest amount of uncertainty (mean of ≤ 0.5 nm up to 40× magnification). Increasing the water flow rate resulted in an increase in mean uncertainty to ≤ 0.6 nm up to 40× with an immersion lens. Observations of a sample through a glass window at 20× magnification in flowing water also yielded increasing uncertainty, with mean values of ≤ 0.5 nm, ≤ 0.8 nm, and ≤ 1.1 nm for flow rates of 0 mL min-1, 15 mL min-1, and 33 mL min-1. Different hologram acquisition rates (12.5 s-1 and 25 s-1) did not significantly impact the uncertainty in the phase. Collecting holograms in single-wavelength versus dual-wavelength modes did impact the uncertainty, with the mean uncertainty at 10× magnification for the same wavelength being ≤ 0.5 nm from the single-wavelength mode compared to ≤ 1.5 nm from the dual-wavelength mode. When the quantified uncertainty was applied to simulated dissolution data, lower limits of measured dissolution rates were found below which the measured data may not be distinguishable from the uncertainty in the measurement. The limiting surface-normal dissolution velocity is -10-11.7 m s-1 for experiments with an immersion lens in flowing water conditions and -10-11.7 m s-1, -10-11.4 m s-1, and -10-11.0 m s-1 for static (0 mL min-1), slow (≤ 15 mL min-1), and fast (≤ 109 mL min-1) flowing water conditions in experiments with a glass window, respectively. The data presented by this study will allow for better experimental design and methodology for future dissolution or precipitation studies using DHM and will provide confidence in the data produced in postprocessing.