Search

This paper describes a preliminary method for the classification of annealed and unannealed polyetherketoneketone (PEKK) components manufactured using a material extrusion three-dimensional (3D) printing process. PEKK is representative of a class of high-performance thermoplastics that are increasingly employed as feedstocks for use in 3D printing. PEKK components may be used continuously at elevated temperatures, are chemically resistant, and able to withstand large mechanical loads. These properties render PEKK suitable as a metal component replacement in aerospace applications, high-temperature industrial applications, and surgical implants. The structure of PEKK is semi-crystalline with the specific crystallinity correlating to the final properties during application, making determination of this property crucial. This study compares three different signal processing techniques intended to distinguish annealed (high crystallinity) from unannealed (low crystallinity) components using backscattered ultrasound. The first is energy-based and is unable to detect annealing. The second two are based on different entropies of the backscattered signal: a limiting form of Renyi's entropy and a limiting form of joint entropy. The joint entropy values for the annealed and unannealed specimens fall into two non-overlapping intervals and have a statistical separation of two standard deviations.

Selective laser sintering methods are workhorses for additively manufacturing polymer-based components. The ease of rapid prototyping also means it is easy to produce illicit components. It is necessary to have a data-calibrated in-situ physical model of the build process in order to predict expected and defective microstructure characteristics that inform component provenance. Toward this end, sintering models are calibrated and characteristics such as component defects are explored. This is accomplished by assimilating multiple data streams, imaging analysis, and computational model predictions in an adaptive Bayesian parameter estimation algorithm. From these data sources, along with a phase-field model, bulk porosity distributions are inferred. Model parameters are constrained to physically-relevant search directions by sensitivity analysis, and then matched to predictions using adaptive sampling. Using this feedback loop, data-constrained estimates of sintering model parameters along with uncertainty bounds are obtained.

Future advances and usage of all-organic polymeric materials with permanent void spaces and high surface areas, in applications such as separations or as supports, depends heavily on the development of processing techniques to produce complex geometry objects. Here, the high free volume glassy microporous polymer PIM-1 was fabricated, as a major component in a polymer blend, into complex and customizable 3D objects by fused filament fabrication (FFF). PIM-1 was found to be compatible with polycaprolactone (PCL) and polylactic acid (PLA) and thus could be processed by extrusion into filaments with high loadings of PIM-1 (50% by mass). Ternary PCL/PLA/PIM-1 composite filaments provided an optimal balance of durability and melt flow characteristics for consistent FFF 3D printing of intricate structures. As printed, the micropores of PIM-1 were blocked and inaccessible to N2 during sorption experiments; however, the ternary composite structures displayed significant meso- and macroporosity and nanostructured ...

Polyetherketoneketone (PEKK) has superior physical properties to most available thermoplastics compatible with material extrusion-based 3D printing. The performance of fused filament fabrication (FFF) compatible PEKK has been detailed primarily as a function of varying the isomer ratios composing the co-polymer structure. PEKK composite or blend development for AM has received limited attention, yet this strategy is attractive for further performance tailoring and to address challenges associated, for example, with shrinkage upon crystallization. Here, we report the integration of three grades of mica platelets into PEKK at 10% and 30% mass loadings to generate an array of filament feedstocks that were used to print objects with a simple FFF machine. The effects of mica coating chemistry on the compatibility with PEKK and resulting properties are described. Mica fillers have only subtle influence on the FFF relevant melt rheological properties inherent to PEKK. Pigment micas at high loadings reduce the melting temperature of PEKK without shifting its glass transition temperature or inducing undesirable crystallization during processing. The printed composites were effectively cold crystallized post-printing similarly to unfilled PEKK resulting in increased dimensional stabilities. All micas, when used as fillers in low and high relative PEKK crystallinities, increased the tensile modulus of parts in correlation to the loading. The microstructural features of a printed composite were compared to unfilled PEKK by use of high-resolution helical micro-computed tomography. Practically, pigment micas can confer a wide range of rich colors to 3D-printed PEKK.

This study aims to establish the relationships between the process parameters, mesostructural features (interlayer neck and void sizes), and the fracture resistance of 3D printed parts. The proposed method enables the decoupling of bond quality and mesostructure effects on the overall fracture behavior. Double cantilever beam specimens of acrylonitrile butadiene styrene (ABS) were designed, printed, and fracture tested. The apparent fracture resistance (Jc,a), the interlayer fracture resistance (Jc,i), and the microstructure were characterized. The fracture results and the microscopic examinations indicate that Jc,a is strongly correlated with the process parameters through both the interlayer adhesion as well as the mesostructure. Nozzle and bed temperatures and layer height were found to have significant effects on the fracture behavior. For instance, the Jc,a increased by 38% with a 20 °C increase in the nozzle temperature. This originated from 15% increase in the interlayer fracture resistance and 23% increase in the actual fracture surface area (interlayer neck size). The quality of interlayer bond was explained in terms of temperature, pressure, and time of the process. This work quantifies the relationships between the printing process and the fracture behavior and provides novel tools and insights in the design and analysis of printed materials. Keywords: Additive manufacturing, 3D printing, Fused deposition modeling, Fracture resistance, Interlayer adhesion, Process parameters

Metal–organic frameworks (MOFs) exhibit exceptional properties and are widely investigated because of their structural and functional versatility relevant to catalysis, separations, and sensing applications. However, their commercial or large-scale application is often limited by their powder forms which make integration into devices challenging. Here, we report the production of MOF–thermoplastic polymer composites in well-defined and customizable forms and with complex internal structural features accessed via a standard three-dimensional (3D) printer. MOFs (zeolitic imidazolate framework; ZIF-8) were incorporated homogeneously into both poly(lactic acid) (PLA) and thermoplastic polyurethane (TPU) matrices at high loadings (up to 50% by mass), extruded into filaments, and utilized for on-demand access to 3D structures by fused deposition modeling. Printed, rigid PLA/MOF composites display a large surface area (SAavg = 531 m2 g–1) and hierarchical pore features, whereas flexible TPU/MOF composites achiev...

3D-printable, flexible, and conductive thermoplastic-based material was successfully developed for strain sensing applications. Thermoplastic polyurethane/multiwalled carbon nanotube (TPU/MWCNT) were compounded, their filaments were extruded, and the sensors 3D printed using fused deposition modeling. Mechanical, electrical, and piezoresistivity behaviors were investigated under monotonous and cyclic loadings. MWNCTs enhanced the printing capability of TPU by increasing its stiffness. Very modest decreases were observed in the elasticity modulus of printed nanocomposites (~14%, compared to that of bulk counterparts), indicating excellent interlayer adhesion and superior performance to those reported in literature. Consequently, the conductivity was largely preserved after printing, in both through-layer and cross-layer directions. The piezoresistivity gauge factors of as high as 176 were achieved under applied strains as large as 100%. A highly repeatable resistance-strain response was also obtained under cyclic loadings. The results demonstrate TPU/MWCNT as an excellent piezoresistive feedstock for 3D printing with potential applications in wearable electronics, soft robotics, and prosthetics, where complex design, multi-directionality, and customizability are demanded. Keywords: Piezoresistivity, Flexible sensors, 3D printed sensors, Fused deposition modeling, Conductive nanocomposites

The significant rise of additive manufacturing (AM) in recent years is in part due to the open sourced nature of the printing processes and reduced cost and capital barriers relative to traditional manufacturing. However, this democratization of manufacturing spurs an increased demand for producers and end-users to verify the authenticity and quality of individual parts. To this end, we introduce an anti-counterfeiting method composed of first embedding engineered nanomaterials into features of a 3D-printed part followed by non-destructive interrogation of these features to quantify a chemical signature profile. The part specific chemical signature data is then linked to a securitized, distributed, and time-stamped blockchain ledger entry. To demonstrate the utility of this approach, lanthanide-aspartic acid nanoscale coordination polymers (Ln3+-Asp NCs)/poly(lactic) acid (PLA) composites were formulated and transformed into a filament feedstock for fused deposition modeling (FDM) 3D printing. In the present case, a quick-response (QR) code containing the doped Ln3+-Asp NCs was printed using a dual-extruder FDM printer into pure PLA parts. The QR code provides a searchable reference to an Ethereum-based blockchain entry. The QR code physical features also serve as defined areas to probe the signatures arising from the embedded Ln3+-Asp NCs. Visible fluorescence emission with UV-excitation was quantified in terms of color using a smartphone camera and incorporated into blockchain entries. Ultimately, linking unique chemical signature data to blockchain databases is anticipated to make the costs of counterfeiting AM materials significantly more prohibitive and transactions between those in the supply chain more trustworthy.

We report the production of flexible, highly-conductive poly(vinylidene fluoride) (PVDF) and multi-walled carbon nanotube (MWCNT) composites as filament feedstock for 3D printing. This account further describes, for the first time, fused deposition modelling (FDM) derived 3D-printed objects with chemiresistive properties in response to volatile organic compounds. The typically prohibitive thermal expansion and die swell characteristics of PVDF were minimized by the presence of MWCNTs in the composites enabling straightforward processing and printing. The nanotubes form a dispersed network as characterized by helium ion microscopy, contributing to excellent conductivity (∼3 × 10−2 S cm−1). The printed composites contain little residual metal particulate relative to parts from commercial PLA-nanocomposite material visualized by micro-X-ray computed tomography (μ-CT) and corroborated with thermogravimetric analysis. Printed sensing strips, with MWCNT loadings up to 15% mass, function as reversible vapour sensors with the strongest responses arising with organic compounds capable of readily intercalating and subsequently swelling the PVDF matrix (acetone and ethyl acetate). A direct correlation between MWCNT concentration and resistance change was also observed, with larger responses (up to 161% after 3 minutes) being generated with decreased MWCNT loadings. These findings highlight the utility of FDM printing in generating low-cost sensors that respond strongly and reproducibly to target vapours. Furthermore, the sensors can be easily printed in different geometries, expanding their utility to wearable form factors. The proposed formulation strategy may be tailored to sense diverse sets of vapour classes through structural modification of the polymer backbone and/or functionalization of the nanotubes within the composite.

Laser sintering (LS) is widely used to produce functional polymeric parts; however, the resulting parts are often limited by their porous structure, and performance of the part may be strongly anisotropic. Relating the structural features of parts to build process conditions or powder feedstock has been explored previously. In contrast, little is known regarding how the unique internal structures of LS parts evolve and relate to their performance later in their life cycle, for example, after use in a real-world operating environment. Here, a tightly controlled LS build process and measurement campaign by standard X-ray computed tomography (XCT), supported by high-resolution synchrotron XCT, was used to benchmark the internal microstructure (e.g. porosity) as a function of four different build orientations in printed polyamide-12 (PA-12) parts. The initial performance of the parts after printing was characterized by tensile testing and dynamic mechanical analysis (DMA). Arrays of PA-12 parts in different build orientations were exposed to steam (under pressure) and air across multiple temperature and time points for the purposes of accelerated aging through oxidative and hydrolytic breakdown. Exposing parts to steam dramatically altered the internal microstructure and functional properties such as the glass transition temperature, tensile properties, and damping behavior. Notably, post-aging XCT revealed large microstructural changes after only 40 h of steam treatment relative to the as-printed specimens. Furthermore, pore reorganization and changes in crystallinity occurred regardless of whether the steam temperature was aggressive enough to induce a significant loss in mechanical properties. The build orientation dependence on the aging rate was minimal with the relative trend in performance persisting across most metrics among the different orientations even after aging.

Fused filament fabrication (FFF) enables production of 3D objects over a range of material compositions at low-cost relative to traditional manufacturing approaches. To date, a limited but growing number of materials are able to be used with FFF, however many applications exist where specific mechanical, thermal, or chemical properties are needed that cannot currently be met with the available feedstock selection. Therefore, a need exists to tune these materials for specific chemical or mechanical properties. One common formulation strategy to address these demanding design parameters is to develop composites or polymer blend filaments. Typically, this is a time-consuming and costly optimization process. Here, we have developed hardware for reproducibly mixing two filaments of similar or dissimilar compositions at the time of printing within individual printed layers. This mixing occurs via software-controlled rotating hardware in the chamber of an extruder’s hot-end. The efficiency of mixing within the printed layers has been characterized in detail as a function of the rotational speed and geometry of the blending hardware. These parameters were exploited to program the ratio and distribution of thermoplastic-based filaments blended within printed extrudate. Example printed specimens were produced with thermoplastic polyurethane (TPU) elastomer blended with rigid polylactic acid (PLA) and nylon blended with PLA. In addition, a conductive carbon nanotube (CNT)–PLA composite was blended as a function of mixer geometry and input feed ratios with non-conductive PLA and resistance values were measured across the resulting printed specimens.

Fabricating complex sensor platforms is still a challenge because conventional sensors are discrete, directional, and often not integrated within the system at the material level. Here, we report a facile method to fabricate bidirectional strain sensors through the integration of multiwalled carbon nanotubes (MWCNT) and multimaterial additive manufacturing. Thermoplastic polyurethane (TPU)/MWCNT filaments were first made using a two-step extrusion process. TPU as the platform and TPU/MWCNT as the conducting traces were then 3D printed in tandem using multimaterial fused filament fabrication to generate uniaxial and biaxial sensors with several conductive pattern designs. The sensors were subjected to a series of cyclic strain loads. The results revealed excellent piezoresistive responses with cyclic repeatability in both the axial and transverse directions and in response to strains as high as 50%. It was shown that the directional sensitivity could be tailored by the type of pattern design. A wearable glove, with built-in sensors, capable of measuring finger flexure was also successfully demonstrated where the sensors are an integral part of the system. These sensors have potential applications in wearable electronics, soft robotics, and prosthetics, where complex design, multi-directionality, embedding, and customizability are demanded.

We combine confocal imaging, microfluidics, and image analysis to record 3D-images of cells in flow. This enables us to recover the full 3D representation of several hundred living cells per minute. Whereas 3D confocal imaging has thus far been limited to steady specimens, we overcome this restriction and present a method to access the 3D shape of moving objects. The key of our principle is a tilted arrangement of the micro-channel with respect to the focal plane of the microscope. This forces cells to traverse the focal plane in an inclined manner. As a consequence, individual layers of passing cells are recorded, which can then be assembled to obtain the volumetric representation. The full 3D information allows for a detailed comparison with theoretical and numerical predictions unfeasible with, e.g., 2D imaging. Our technique is exemplified by studying flowing red blood cells in a micro-channel reflecting the conditions prevailing in the microvasculature. We observe two very different types of shapes: "croissants" and "slippers." Additionally, we perform 3D numerical simulations of our experiment to confirm the observations. Since 3D confocal imaging of cells in flow has not yet been realized, we see high potential in the field of flow cytometry where cell classification thus far mostly relies on 1D scattering and fluorescence signals.

As the desire for wearable electronics increases and the soft robotics industry advances, the need for novel sensing materials has also increased. Recently, there have been many attempts at producing novel materials, which exhibit piezoresistive behavior. However, one of the major shortcomings in strain sensing technologies is in the fabrication of such sensors. While there is significant research and literature covering the various methods for developing piezoresistive materials, fabricating complex sensor platforms is still a manufacturing challenge. Here, we report a facile method to fabricate multidirectional embedded strain sensors using additive manufacturing technology. Pure thermoplastic polyurethane (TPU) and TPU/multiwall carbon nanotubes (MWCNT) nanocomposites were 3D printed in tandem using a low-cost multi-material FDM printer to fabricate uniaxial and biaxial strain sensors with conductive paths embedded within the insulative TPU platform. The sensors were then subjected to a series of cyclic strain loads. The results revealed excellent piezoresistive responses of the sensors with cyclic repeatability in both the axial and transverse directions and in response to strains as high as 50%. Further, while strain-softening did occur in the embedded printed strain sensors, it was predictable and similar to the results found in the literature for bulk polymer nanocomposites. This works demonstrates the possibility of manufacturing embedded and multidirectional flexible strain sensors using an inexpensive and versatile method, with potential applications in soft robotics and flexible electronics and health monitoring.

Additive Manufacturing (AM) is an emerging field with rapid growth. Fused Deposition Modeling (FDM), as an AM method, is becoming increasingly popular. With the ability to create parts from a wide range of thermoplastics, it is necessary to understand the effects of FDM process on the printed part’s mechanical properties for a given material. This paper investigates the mechanical properties of 3D printed TPU parts created by a typical low cost desk-top FDM machine. TPU was first extruded into filament suitable for FDM and printed into samples for tensile tests according to the ASTM 3039 standard. The effects of raster orientation, nozzle temperature, and air gap on the mechanical properties were investigated. The compression-molded samples were used as the baseline. While the printed samples had an overall lower ultimate tensile strength (UTS) compared to the molded samples, the printed samples with a negative air gap showed nearly isotropic material properties, irrespective of raster orientation and nozzle temperature. For samples with a positive air gap, raster orientation had a large influence on the overall UTS. Nozzle temperature did not have much effect on the UTS. When compared to rigid thermoplastics TPU has a much lower glass transition temperature (Tg) at -40° C. This allows for much better interlayer bonding between print lines as TPU is above Tg for the entire printing process.

Additive manufacturing refers to a new technology in which physical parts are directly produced from a computer model by incremental addition of the constituent materials. Fused deposition modeling (FDM) is one of the most common types of additive manufacture processes. The ultimate mechanical performance of FDM printed parts is a function of the interlayer bond quality. Current literature however focuses only on the phenomenological evolution of standard mechanical properties (such as tensile and bending) as a function of printing conditions. Such studies do not provide direct information about the interlayer adhesion and in-practice failure characteristics. In this work, a fracturemechanics- based methodology was used to characterize the fracture resistance of FDM 3D printed Acrylonitrile Butadiene Styrene (ABS) samples as a function of nozzle and bed temperatures. Double cantilever beam (DCB) specimens was printed in such pattern that the applied load exerted only tensile opening stresses at the crack front. This facilitated the measurement of crack growth under pure mode-I condition. A finite element model was then used to obtain the J-integral strain energy release rate values, as a measure of the fracture resistance. Since the crack propagated at the interlayer in all the cases, the fracture resistance was a direct indication of the interlayer adhesion. The results revealed that the critical crack growth load, the actual fracture surface area (governed by printed mesostructure) and the apparent fracture resistance all increased when the nozzle or bed temperature was increased; the nozzle temperature showed a much stronger effect. The layer-to-layer adhesion, as reflected by the interlayer fracture resistance, did not show monotonous increase with the temperatures and appeared to level off at higher temperatures, indicating that complete interlayer fusion was achieved. This work provides insight into and characterizes the relationships between the 3D printing conditions, the resultant mesostructure, the apparent fracture resistance and the interlayer adhesion in FDM 3D printed materials.

In 32 patients presenting symptoms of arterial occlusive disease, 50 lower limbs were examined both by ultrasonography and angiography (DSA). Sonography was performed using a 5.0 MHz real-time scanner; common femoral, superficial femoral and deep femoral arteries were visualized continuously in whole length. In 84% both the results from sonography and digital subtraction angiography verified or excluded arterial occlusion. Since lack of pulsation is the ultrasonic criterion of occlusion, real-time ultrasound does not differentiate between haemodynamically effective high-grade stenosis and total occlusion.

The radiological imaging of the respiratory tract by bronchography has apparently lost in importance since the introduction of newer imaging methods. Indications for and results of bronchography, performed after bronchoscopy with a flexible bronchoscope under local anesthesia, were analysed in 115 patients. In 68 the bronchography had been performed because of suspected bronchiectasis, in the others because of hemoptysis, cough or infiltration of unclear etiology. In 43% of patients who had undergone bronchography bronchiectasis was indeed found, in 47% there were isolated or additional changes in the bronchial system. In 70% the examination had furthered the diagnosis. The described method of bronchography was not significantly more uncomfortable than flexible bronchoscopy alone. Combined bronchoscopy and bronchography is thus a valuable procedure in the diagnosis of pneumonological abnormalities.

Bei 6 Patienten mit hepatisch metastasier-ten gastrointestinalen Tumoren des neuroendokrinen Typs, darunter je ein Inselzellkarzinom und Gastrinom des Pankreas, ein sog. kloakogenes Analkarzinom und 3 Karzinoide des Dunndarms, wurden spontane Gewebeverflussigungen innerhalb echoreicher Lebermetastasen sonographisch dokumentiert. In der sonomorpho-ZEI-ogischen Klassifikation handelte es sich um “Bulls-eye”-Lasionen ohne Kokardenmerkmal. Zytosta-tische Chemotherapie blieb ohne sonographisch belegbare Auswirkungen. In unserem Krankengut waren Ein-schmelzungserscheinungen bei diesen hochdifferenzierten Tumormetastasen relativ viel haufiger als bei schnell proliferierenden Malignomen mit ca. 1 : 40, ohne das dem Nachweis einer Einschmelzung aber eine prognostische Bedeutung zukame. Bei Unkenntnis eines Primartumors sind in die sonographische Differentialdiagnose auch entzundliche Prozesse einzubeziehen. In six patients with hepatically metasta-sised gastrointestinal tumours of neuroendocrinal origin, including one each islet cell carcinoma and gastrinoma of the pancreas, one cloacogenic carcinoma (a rare type of anal cancer), and three carcinoid tumours of the small bowel, spontaneous liquefaction inside echogenic liver metastases was demonstrated by ultrasound. The hepatic lesions were classified as being of “bull's-eye-” shape without “badge” pattern. Chemotherapy had no effect on their ultrasonographic imaging. With regard to our observations, liquefyng processes were far more common in these well-differen-tiated tumour metastases than in poorly differentiated fast-proliferating malignancies (about 1:40). Assessment of liquefaction, however, has obviously no influence on the prognosis of progress speed. Ultrasonographic dif-ferential diagnosis includes focal inflammatory disease of the liver, if there is no evidence of a primary tumour.

This article is reproduced from the previous edition, volume 21, pp. 14106–14110, © 2001, Elsevier Ltd., with an updated Bibliography section supplied by the Editor.

The preclinical diagnosis of shock is still based on the patient's history, the physical examination, the injury pattern and a few hemodynamic parameters available in the emergency set-up. The clinical picture is characterised by hypotension and tachycardia, tachypnoe and dyspnoea as well as cerebral impairment. Results from recent clinical trials indicate, that a adapted and specific therapeutic approach for the various shock forms is necessary. In case of traumatic hypovolemic-hemorrhagic shock it is of particular relevance if penetrating trauma and/or uncontrolled bleeding exists. Under these conditions an immediate definite surgical treatment is required ("scoop and run") and a moderate hypotension should be tolerated. ("treat and run"). Fluid substitution and therapy with catecholamines should be used conservatively. In all other forms of shock the treatment approach can and should be more aggressive in order to improve microvascular perfusion as early as possible. Besides adequate fluid resuscitation in a combination of crystalloid and colloid solutions catecholamines and-under specific circumstances-also vasopressin should be used. Of utmost importance in the pre-clinical management of patients in shock is the optimal selection of the centre that the patient is referred to in order to establish the fastest and best possible definite treatment for the patient.

Durch den Einsatz der hochauflosenden Computertomographie in der Diagnostik intrakranieller Erkrankungen nimmt die Beobachtungshaufigkeit idiopathischer Stammganglienverkalkungen zu. Ziel der vorliegenden Arbeit war es, den Zusammenhang zwischen idiopathischen Stammganglienverkalkungen und klinischen Symptomen zu uberprufen. Bei 2318 computertomographisch untersuchten selektierten Patienten fand sich eine Pravalenz von 12,5%, sowohl beim psychiatrisch, wie auch beim nicht psychiatrisch erkrankten Teil der Patienten. Hauptlokalisation war der Globus pallidus (96,4%). Eine Korrelation der Verkalkungen zu den mit dem Begriff “Fahr-Syndrom” in Verbindung gebrachten Symptomen konnte, ebenso wie eine Grosenabhangigkeit, fur die beobachteten Auspragungen nicht hergestellt werden.

A 60-year-old woman with metastatic lobular carcinoma of the left breast and Sjogren's syndrome developed a tumor of the right breast. Histology showed an amyloid tumor. Further studies showed tumor-like amyloidosis of the left breast in apposition to the carcinoma. Immunoelectrophoresis showed IgG gammopathy. There was no Bence-Jones protein in the urine. The presence of amyloid was confirmed with congo red staining and electron microscopy. Systemic amyloidosis, which often arises from monoclonal B-cell dysplasia (e.g., multiple myeloma) or rheumatoid arthritis, can cause diffuse, focal, or tumor-like deposits in the breast. Amyloid tumors, whose etiology is unclear, are rare in the breast and usually mistaken for carcinomas. We found no association between Sjogren's syndrome and amyloidosis or between breast cancer and amyloid tumors. A localized amyloid tumor does not need to be excised and should be distinguished from systemic amyloidosis, which requires treatment.

The goal of this paper is to show the behavior of effective marginal tax rates relative to statutory marginal tax rates within the rate structure of the present federal income tax regime. Understanding the behavior of effective marginal rates is important as these rates are a significant component of tax planning and decision making. Statutory marginal tax rates are explicitly stated in published rate schedules. Various deductions, exemptions and credits involved in determining the tax liability are phased out as gross income increases. These restrictions result in effective marginal tax rates that can exceed respective statutory rates. Substantial divergence between effective and statutory rates can occur when multiple phase-out provisions overlap and interact. This study develops an algebraic model using tax return information that converts statutory to effective marginal rates. Policy implications concerning simplifying the effective rate structure are also discussed.

In 15,645 consecutive ultrasound examinations of the abdomen (1986 to 1988), free fluid in the peritoneal cavity was found in 247 patients by internal trial during 397 sessions (= 2.5%). Most frequent basic diagnosis for the reason of this symptom were tumorous diseases (99 patients corresponding to 40.1%), cirrhosis of the liver (52 patients corresp. to 22.1%) and heart failure (31 patients corresp. to 12.6%, among these complex gayprooft myocardial insufficiency 24, right heart failure 7). Ovarian cysts or cystomas (7), acute/chronic-recurrent pancreatitis (6), Crohn's disease (3), infections (3), rheumatoid disorders (3), nephrotic syndrome (2), and extra-uterine pregnancy (2) were more rarely represented. In 23 patients (corresp. to 9.3%) the cause of an ascites remained obscure. Among these, a high prevalence of the female sex in the premenopausal age was remarkable with a score of 20:3 (statistically significant difference in terms of the other patients of our group). This observation suggests that an ovarian factor plays a role in the development of ascites in the absence of other evident causes. The literature implies that endometriosis is rather prominent, followed by oligosymptomatic infections or inflammatory diseases.

Die Sensitivitat fur den Nachweis regionarer Lymphknotenmetastasen kolorektaler Karzinome wurde unter Anwendung verschiedener Kriterien fur das N1-Stadium an Patienten mit histologisch gesichertem Lymphknotenbefund untersucht. Fur das Kriterium N1=Lymphknoten (LK) >1 cm betrug die Sensitivitat 47%. Fur N1=LK >1 cm/vermehrte Anzahl LK

The frequency, presentation, diagnosis and clinical course of Pneumocystis carinii infections (PCI) were studied during aerosolized pentamidine prophylaxis (AP) and its impact on the spectrum of AIDS-related and other pulmonary infections in HIV-infected hemophiliacs. We conducted an open study on primary (PP) and secondary (SP) AP. Breakthrough P. carinii infections (BPCI) and other infectious complications were analyzed retrospectively. Hemophiliacs without prior P. carinii pneumonia (PCP) who had been reluctant to any prophylaxis and who developed PCP served as control group. Statistical analysis of the efficacy of prophylaxis was performed by calculating confidence intervals of binomial p. Of 73 hemophiliacs (56 on PP and 17 on SP) 10 developed BPCI (7 in PP and 3 in SP) during a mean observation time of 14.9 months (range 0.5-30); total 13.6% (6.7%; 23.7%), PP 12.5% (5.1%; 24%), SP 17.6% (3.7%; 43.4%), confidence intervals at a level of 95%. Three BPCI presented atypically with cavitation (1), pneumothorax (2), Pneumocystis pleuritis (1), dissemination (2) as compared to none in the control group. Sensitivity of bronchoalveolar lavage (BAL) was 88.9%, specificity 100% (both 100% in the control group). PCP was the leading AIDS manifestation (21.3%), CNS manifestations taken together were more frequent (36.2%). Bacterial pneumonia was the most frequent respiratory infection. One patient of the study group with recurrent pneumothorax possibly died of BPCI as compared to no BPCI-related deaths in the control group. Efficacy of prophylaxis in hemophiliacs was comparable to other risk groups. AP alone may be insufficient for the control of PCI in patients with long-term profound immunodeficiency, especially in SP. 30% of BPCI presented atypically.(ABSTRACT TRUNCATED AT 250 WORDS)

The mechanical properties of tissues are increasingly recognized as important cues for cell physiology and pathology. Nevertheless, there is a sparsity of quantitative, high-resolution data on mechanical properties of specific tissues. This is especially true for the central nervous system (CNS), which poses particular difficulties in terms of preparation and measurement. We have prepared thin slices of brain tissue suited for indentation measurements on the micrometer scale in a near-native state. Using a scanning force microscope with a spherical indenter of radius ∼20μm we have mapped the effective elastic modulus of rat cerebellum with a spatial resolution of 100μm. We found significant differences between white and gray matter, having effective elastic moduli of K=294±74 and 454±53Pa, respectively, at 3μm indentation depth (n(g)=245, n(w)=150 in four animals, p

A transparent poly (ether urethane) (PEU) was considered for use as a foldable intraocular lens material. The PEU was found to possess excellent mechanical, optical, and surface characteristics for this application. In vitro hydrolytic and ultraviolet aging studies suggested the PEU to be tolerant to conditions simulating 3-10 years of normal intraocular exposure. Different behavior was obtained, however, from intraocular and subcutaneous implantation of the PEU. After 6 months of intraocular exposure in the feline model, prototype PEU lenses had lost most or all of their optical resolving power. SEM analysis demonstrated scattered pitting and cracking on the lens surfaces. Degradation was found to be more extreme after as little as 30 days of subcutaneous exposure in rabbits. Severe pitting over the entire surface of implanted flat PEU specimens was observed by SEM. Macroscopic examination showed the samples to be frosty in appearance. It was postulated that the subcutaneous implant environment provides an accelerated in vivo model for materials intended for intraocular use. A minimum acceleration of 6-10x was estimated on a preliminary basis. The PEU studied here was found to be unsuitable for use as a foldable intraocular lens material.

Diagnostic assessment of focal pleural mass requires CT examination, particularly in follow-up of anamnestic tumour conditions. Since 1976 well-delineated pleural masses that were suspicious for malignancy on chest films, were identified in 11 patients as lipomas, using CT. They showed semicircular, oval or polygonal shape, but no really "spheric" aspect on biplane chest films. Main diameters of these masses were 2.5 to 6 cm and only once 11 cm. Density values mostly ranged from -110 to -70 HE (min. -133, max. -22 HE) in nonenhanced CT studies. Findings were localised adjacent to the parietal pleura seven times (in one patient two separate findings) and to the diaphragmatic pleura five times. In 7751 CT examinations of the chest, the incidence of pleural lipomas was 0.14%, their prevalence concerning solid pleural lesions being 5.3%. Among all intrathoracic lipomas those in mediastinal and paracardial location respectively were definitely more often (30 patients).

The design of feedback (or recurrent) neural networks to produce good solutions to complex optimization problems is discussed. The theoretical basis for applying neural networks to optimization problems is reviewed, and a design rule that serves as a primitive for constructing a wide class of constraints is introduced. The use of the design rule is illustrated by developing a neural network for producing high-quality solutions to a probabilistic resource allocation task. The resulting neural network has been simulated on a high-performance parallel processor that has been optimized for neural network simulation. >

Credibility (or lack of it) ’ m 01 ernment g . policy announcements is important. Hence, the task the authors have set for themselves in this paper-to analyze the content, of the policy undertakings issued by 15 annual economic summit meetings of the seven major economic powers, and measure the extent to which they have been honored-is a lauda,ble one. It is also a difficult one, because summit statements are oft,en made purposely vague, in order to avoid the embarrassment that would occur if a clear and unambiguous commitment were not honored. (Remember the so-called forecaster’s rule: “When forecasting, give t,hem a. number, or give them a date, but never both.“) The authors’ method has three steps. For ea.ch statement of a policy undertaking, (1) decide whether it implies a commitment or not (in 203 cases in 15 yea.rs they decided it) did); (2) If so, wait a year to see what happened; and then (3) g’ lve a score between -1 and +l to indicate the degree of compliance. The unweighted a.verage of the scores given for all commitments was a.bout 0.131 (it was a.bout 0.27 if each country’s scores were weighted by its GNP: thus, the bigger countries were scored as slightly less compliant). The scoring was done a.s follows. For each commitment, two benchmark points on the scale were set, by arbitra.rily assigning a score of zero to an outcome that was judged to represent no movement toward compliance, and a score of +1 to an outcome t,hat was judged to represent ideal compliance. (The way “ideal compliance” is defined is crucial to the results, as will be