Sharp Cut Research Articles

How do jet time, pressure and bone volume fraction influence the drilling depth when waterjet drilling in porcine bone?

Using water jets for orthopedic procedures that require bone drilling can be beneficial due to the absence of thermal damage and the always sharp cut. Previously, the influence of the water jet diameter and bone architectural properties on the drilling depth have been determined. To develop water jet instruments that can safely drill in orthopedic surgery, the impact of the two remaining primary factors were determined: the jet time (tjet [s]) and pressure (P [MPa]). To this end, 84 holes were drilled in porcine tali and femora with water jets using Ø 0.4mm nozzle. tjet was varied between 1, 3 and 5s and P between 50 and 70MPa. Drilling depths Lhole (mm), diameters Dhole (mm) and the volume of mineralized bone per unit volume (BV/TV) were determined with microCT scans.A non-linear regression analysis resulted in the predictive equation: Lhole= 0.22 * tjet0.18 * (1.2–BV/TV) * (P–29) (R2=0.904).The established relation between the machine settings and drilling depth allows surgeons to adjust jet time and pressure for the patient׳s BV/TV to drill holes at a predetermined depth. For developers, the relation allows design decisions to be made that influence the dimensions, flexibility and accuracy of water jet instruments. For a pressure of 50MPa, the potential hole depth spread indicated by the 95% confidence interval is <1.6mm for all tested jet times. This maximum variance is smaller than the accuracy required for bone debridement treatments (2–4mm deep), which confirms that water jet drilling can be applied in orthopedic surgery to drill holes in bone with controlled depth.

Ensemble of randomized soft decision trees for robust classification

For classification, decision trees have become very popular because of its simplicity, interpret-ability and good performance. To induce a decision tree classifier for data having continuous valued attributes, the most common approach is, split the continuous attribute range into a hard (crisp) partition having two or more blocks, using one or several crisp (sharp) cut points. But, this can make the resulting decision tree, very sensitive to noise. An existing solution to this problem is to split the continuous attribute into a fuzzy partition (soft partition) using soft or fuzzy cut points which is based on fuzzy set theory and to use fuzzy decisions at nodes of the tree. These are called soft decision trees in the literature which are shown to perform better than conventional decision trees, especially in the presence of noise. Current paper, first proposes to use an ensemble of soft decision trees for robust classification where the attribute, fuzzy cut point, etc. parameters are chosen randomly from a probability distribution of fuzzy information gain for various attributes and for their various cut points. Further, the paper proposes to use probability based information gain to achieve better results. The effectiveness of the proposed method is shown by experimental studies carried out using three standard data sets. It is found that an ensemble of randomized soft decision trees has outperformed the related existing soft decision tree. Robustness against the presence of noise is shown by injecting various levels of noise into the training set and a comparison is drawn with other related methods which favors the proposed method.

Universal Band Pass Sampling Algorithm for Integration of Multiple Wireless Technologies Using Software Defined Radio Platform

Software Defined Radio (SDR) architecture allows us to integrate different mobile technologies using common hardware but with different software modules. To achieve this, we need to keep the signal in digital form for as much portion of the circuitry as possible, so that the implementation could be carried out by programmable digital processors. For this purpose, the incoming radio frequency (RF) signal is down converted to baseband spectrum using band pass sampling method. Research works carried out so far in this field have developed a few algorithms for band pass sampling. But, these algorithms are not much useful for most of the mobile communication systems and they use complex methodology for computing the sampling frequency values. In order to use the SDR platform to integrate all current wireless technologies, an efficient, cost effective and less complex algorithm that can be labelled as universal band pass sampling algorithm is developed in this paper for multiple mobile systems. This algorithm is based on a novel idea of inserting guard bands between the signals which reduces the design complexities of perfect ADC and sharp cut off filters. Using this algorithm, valid sampling frequency ranges and corresponding IF values are calculated for down converting RF signals. The algorithm is tested for six RF signals of different wireless technologies which are integrated and simultaneously down converted using SDR based front end receiver and thus the system multiplies the base station capacity by a factor of six. The simulation results are obtained and shown in this paper which proves that the algorithm developed works well for most of the wireless technologies.

Mutilation of Body after crime

Introduction: Mutilation of the body after death is considered a more heinous crime than the murder itself. After a homicide, dismemberment and mutilation is done to conceal the body or to dispose it away without being noticed. Case explanation: The present case unfolds one such crime where a 70 year old retired army doctor killed his 62 year old wife and mutilated her body into multiple pieces. Autopsy revealed multiple split lacerated wounds on her occipital area, parietal area, temporal area and forehead. Several depressed fractures were found on her skull bone underlying the lacerated wounds. Brief discussion: As the body pieces were recovered after several days of her death, the internal organs were grossly decomposed. The brain matter was missing from the exposed cranial cavity. The cause of death was opined to be due to the head injuries consequent upon some hard blunt force impact. The manner of death appeared homicidal as most of the injuries were on the vertex area. The dismembered ends had some sharp cuts and some irregularities suggesting the use of axe, saw and knife as alleged.

Epidemiology of injury and risk factors among adults in Guizhou province, 2010

To understand the epidemiologic characteristics of injury among adults in Guizhou province. A questionnaire survey was conducted among 9 280 residents aged ≥18 years selected though multistage cluster random sampling in Guizhou to collect the information about their demographic characteristics and incidence data of injury. Logistic regression analysis was done to identify the risk factors. The incidence of injury was 3.5% in the adults surveyed (3.6% in males, 3.4% in females). The incidences of injury in both urban area and rural area were same (3.5%). The incidence of injury was 3.9% in age group 18-44 years, 2.7% in age group 45-59 years, and 3.5% in age group≥60 years, the differences among different age groups were statistically significant (χ2=7.949, P=0.019). The top three injury causes were fall (35.0%), road traffic accident (20.0%) and animal bite (19.2%). The top three injury causes in the elderly were fall (59.3%), animal bite (22.0%) and sharp instrument cut (10.2%). Among the elderly, the incidence of road traffic injury was higher in males (1.1%) than in females (0.3%), the difference was statistically significant (χ2=18.156, P=0.000). The incidence of fall in urban area (1.6%) was higher than that in rural area (1.1%), the difference was statistically significant (χ2=4.616, P=0.032). Drinking and drunk driving, fatigue driving, smoking and gender were the influencing factors for injury. Injury related high risk behaviors were common in adults in Guizhou, it is necessary to develop effective intervention measures to prevent injury.

A MESOLITHIC HUMAN FIGURINE FROM RIVER PÄRNU, SOUTH-WEST ESTONIA: A CENTURY-OLD PUZZLE OF IDOLS, GODDESSES AND ANCESTRAL SYMBOLS

Introduction In the early years of the twentieth century, an antler human figurine (PaMu 1 A: 501) was found in River Parnu, south-east Estonia (Fig. 1). It is one of the rare archaeological finds from Estonia that already from the very first publications (Ebert 1913; Gluck 1914) reached several wider studies about European archaeology (Tallgren 1922; Childe 1925; Gimbutas 1956). Due to some reasons, interest in the object was lost during the second part of the century. It was mentioned only passingly in a study about the Stone Age religion in Estonia (Jaanits 1961) and it has not been brought up at all in Eesti esiajalugu (Estonian Prehistory, Jaanits et al. 1982), which was a major study of Estonian archaeology for decades. Most likely, one of the reasons for such a random use was the absence of dating and therefore a speculative relationship any specific archaeological period and culture. [FIGURE 1 OMITTED] The figurine The 10 cm tall human sculpture is made of an elk antler and it was created only very simple means. Two different ways of processing can be distinguished: cutting to create sharper edges and smoothing to express softer contours. With three wide grooves, the knees, waist and neck have been marked, and a sharp cut the flat breast and chin are shown. The mouth has been cut in so that the round chin emerges. The face together the hooknose has been designed by polishing. Eyes have not been depicted and this makes the statuette different from all other Stone Age figurines. Although slightly younger, the human figurines from the East European forest zone of the Late Mesolithic-Early Neolithic always have eyes and/or strong and protruding eyebrows (Butrimas 2000, 12). Eyes are marked usually drilled holes, but it seems that the eyebrows alone were also good enough for that purpose (see Fig. 4: 6, 7, 9). The face of the Parnu figurine has only a nose and a mouth, leaving the upper part of the face plane. In addition to the eyes, the sculpture is also missing details of the body. While the rest of the human figurines from the northern part of Eastern Europe have their hands marked lines or carved, then in the case of the Parnu example it had not even been tried. Also legs are missing, and therefore Marija Gimbutas has characterized the figurine as with a single leg (Gimbutas 1956, 189). According to Gimbutas, the absence of legs and hands is common in the art of the Stone Age East European forest zone (ibid.). Still, the claim does not hold true and limbs, either more or less elaborated, have been marked in the majority of human figurines dated to the Stone Age. The figure has been made from the tip of an antler branch. One can only agree the suggestion by Eduard Gluck that the antler branch was longer at the time of carving and it was used as a handle until it was cut (and broken) shorter from the pate after it had been finished (Gluck 1914, 265). Because of that the surface of the pate remained uneven and a groove was formed. Find context It is not known when exactly the figurine was found. It was first mentioned by Max Ebert (1913, 520) as an example from the private collection of Friedrich Rambach, but the proper publication and description was presented by Eduard Gluck a year later (1914, 265 f.). According to them, it can be assumed that the figurine was found either in 1911 or 1912. The antler object was found from the bottom of River Parnu in the town of Parnu, upstream of the one-time brick factory Koksi (Gluck 1914, 266), in the so-called Pauka crook, which is one of the richest find places of Estonian Stone Age bone and antler objects. The finds were collected mainly at the beginning of the 20th century, when sand and gravel was quarried from the bottom of the river. During the shovel-based quarrying, a rich collection of ancient artefacts was found from the Pauka crook. This site, which initiated the creation of many privately held collections, contained both hunting and fishing gear, but also axes, processed and unprocessed bone and antler, etc. …

Determination of the Fracture Toughness of Optomechanical Devices

Static fracture toughness characteristics are traditionally determined in tests of standard notched specimens using a P-V curve, where P is the load and V is the notch-opening displacement. This curve has a characteristic point Q. At the load PQ corresponding to this point, the crack starts to propagate. For this load, the fracture toughness characteristics are then calculated. In brittle (elastic) fracture, the P-V curve at the onset of crack propagation has an extremum (or a local extremum), from whose ordinate PQ is determined with sufficient accuracy. In ductile and elastic-ductile fracture, P-V curves are monotonically increasing, and PQ is calculated using the 5% secant offset method without taking into account the characteristics of the material, so that the PQ is determined inaccurately. To improve the accuracy of PQ determination, we propose a thermographic method for determining the fracture toughness of metals. This method involves plotting the load P against the temperature change ΔТ over a relatively short period of time at the notch tip. This plot is then transformed to a P-ΔS curve, where ΔS is the specific entropy increment at the notch tip, which is calculated through ΔТ. This thermodynamic diagram has a characteristic step at the beginning of crack propagation, and from the ordinate of this step, PQ can be determined much more accurately. Furthermore, in the thermographic method, the preparation of test specimens can be simplified by replacing the process of growing a fatigue crack at the tip of a notch by making a sharp cut, which provides significant time savings. Statistical processing and comparison of test results of steel 20 specimens using the conventional and thermographic methods have shown the advantages of the thermographic method in accuracy and complexity.

El lugar de visigodos y omeyas en la historiografía de los siglos XIX y XX. Aportaciones a un debate sobre continuidad y ruptura

This text aims to analyze the evolution during the nineteenth and twentieth centuries paradigms of the historical division between Antiquity and the Early Middle Ages and its impact on Spanish archeology. In a special will be described how and when the concept of late antiquity was introduced, replacing the previous paradigms. Also we try to analyze whether the continuity and process elements connected thereto affect the origins of al-Andalus, discussing the existence of an abrupt and sharp cut from the Arab and Berber invasion.

Online Higher Education: Beyond the Hype Cycle

When two Silicon Valley start-ups, Coursera and Udacity, embarked in 2012 on a bold effort to supply college-level courses for free over the Internet to learners worldwide, the notion of the Massively Open Online Course (MOOC) captured the nation's attention. Although MOOCs are an interesting experiment with a role to play in the future of higher education, they are a surprisingly small part of the online higher education scene. We believe that online education, at least online education that begins to take full advantage of the interactivity offered by the web, is still in its infancy. We begin by sketching out the several faces of online learning—asynchronous, partially asynchronous, the flipped classroom, and others—as well as how the use of online education differs across the spectrum of higher education. We consider how the growth of online education will affect cost and convenience, student learning, and the role of faculty and administrators. We argue that spread of online education through higher education is likely to be slower than many commenters expect. We hope that online education will bring substantial benefits. But less-attractive outcomes are also possible if, for instance, legislators use the existence of online education as an excuse for sharp cuts in higher education budgets that lead to lower-quality education for many students, at the same time that richer, more-selective schools are using online education as one more weapon in the arms race dynamic that is driving costs higher.

Retrospective analysis of acute hand injuries in an academic tertiary hospital that need plastic surgeon consultation

Hand surgery covers a major area of plastic surgery practice. To our knowledge, there is no publication directly investigating the characteristics of hand injuries that plastic surgery consultation was requested, which could be an essential information to guide the plastic surgery education programs. This study determined the features of the hand injuries presented to the plastic surgery department during a year from an academic trauma hospital in Turkey. Epidemiological information of the patients with hand injuries who were admitted to the emergency department of an academic tertiary hospital and needed plastic surgery consultation was evaluated. Patients were analyzed retrospectively in terms of gender, distribution of age, occupation, mechanism of injury, cause of injury, injured soft tissue structures, and duration of hospitalization. One thousand and forty-three (83.7 %) of the 1246 patients included in the study were male and 203 (16.3 %) were female. The mean age of patients was 32. The most common injured structure were the tendons with a rate of 41.2 %. The tendons were followed by fractures, tissue defects, nail injuries, nerve injuries, and vascular injuries with a rate of 18.8, 16.6, 10, 8.3, and 5.3 %, respectively. The most frequent mechanism of injury was crush type (38.6 %) followed by blunt cut (26.9 %), sharp cut (25.9 %), combined (4.8 %), and avulsion injuries (3.8 %). 7.8 % of the patients with hand injuries had amputations. Despite the limitations, our study can reflect emergency hand injuries that a plastic surgeon may be faced within a tertiary care center. By our work, a plastic surgeon will be aware of demographic features of a patient with a hand injury presented by the emergency department. Level of Evidence: Level IV, risk/prognostic.

A method of using a sharp cut and pointy electro-optic material for massive reduction of Vπ voltage

Half wave voltage or Vπ voltage plays an important role for application of electro-optic modulator in data or signal processing. The depth of the modulation by an electro-optic modulator depends on its Vπ voltage. Several techniques of reducing the Vπ voltage of an electro-optic modulator have already been reported. Here in this paper the authors propose a new scheme for reducing the Vπ voltage of a modulation to a very small value by using a sharp cut and pointy crystal as electro-optic modulator.

Performance measurement analysis of various cone flow meters with various beta edge types and flow field parameters

The beta edge, as one part of the cone element in cone flow meters, has several types. Cone flow meters with different beta edges have different applications and measurement performance. The sharp angle, corner cut and arc are the most common forms of beta edges used in cone flow meters. Their structures are analyzed without changing other parameters. Through theoretical analysis of their hydromechanics, a conclusion can be drawn that the discharge coefficient linearity error and permanent pressure loss in cone flow meters can be predicted based on the consistency in the recirculation quantity and the dissipation function value. The research objects are cone flow meters with different beta edge forms whose inner tube diameter is 100mm and whose β values are 0.45, 0.55 and 0.65. The cone wake flow field characteristics were obtained and analyzed using the CFD method. Different beta edges cause different changes to the recirculation quantity and the dissipation in the cone wake flow region. Based on the theoretical prediction, the corner cut beta edge has the best discharge coefficient linearity error and relatively small permanent pressure loss. The accuracy of this prediction was experimentally verified. The experimental results demonstrate that the sharp-angle beta edge achieves the best performance in mechanical processing consistency, while the arc beta edge is the worst.

Joint Planck and WMAP assessment of low CMB multipoles

The remarkable progress in cosmic microwave background (CMB) studies over past decade has led to the era of precision cosmology in striking agreement with the ΛCDM model. However, the lack of power in the CMB temperature anisotropies at large angular scales (low-ℓ), as has been confirmed by the recent Planck data also (up to 0ℓ=4), although statistically not very strong (less than 3σ), is still an open problem. One can avoid to seek an explanation for this problem by attributing the lack of power to cosmic variance or can look for explanations i.e., different inflationary potentials or initial conditions for inflation to begin with, non-trivial topology, ISW effect etc. Features in the primordial power spectrum (PPS) motivated by the early universe physics has been the most common solution to address this problem. In the present work we also follow this approach and consider a set of PPS which have features and constrain the parameters of those using WMAP 9 year and Planck data employing Markov-Chain Monte Carlo (MCMC) analysis. The prominent feature of all the models of PPS that we consider is an infra-red cut off which leads to suppression of power at large angular scales. We consider models of PPS with maximum three extra parameters and use Akaike information criterion (AIC) and Bayesian information criterion (BIC) of model selection to compare the models. For most models, we find good constraints for the cut off scale kc, however, for other parameters our constraints are not that good. We find that sharp cut off model gives best likelihood value for the WMAP 9 year data, but is as good as power law model according to AIC. For the joint WMAP 9 + Planck data set, Starobinsky model is slightly preferred by AIC which is also able to produce CMB power suppression up to 0ℓ⩽3 to some extent. However, using BIC criteria, one finds model(s) with least number of parameters (power law model) are always preferred.

Replantation of the upper extremity: current concepts.

Replantation is the process of reattaching amputated parts. Relative indications for replantation in the upper extremity include amputation of the thumb or multiple digits as well as amputations proximal to zone II and pediatric finger amputations at any level. Preoperatively, the part should be sealed in a bag and placed on ice; maximum ischemia times are approximately 12 hours of warm and 24 hours of cold time for digits, with shorter times tolerated for amputations at more proximal levels. With multiple digit involvement, an assembly line approach is used in the operating room. Postoperatively, close attention must be paid to detect thrombosis because secondary ischemia times are shorter. Success rates vary; survival is predicted in part by the mechanism of injury, with sharp cut injuries having better outcomes. There is no consensus on appropriate postoperative anticoagulation, the number of vessels that must be anastomosed, or whether replantations should be centralized or performed in every hospital.

On the scalar consistency relation away from slow roll

As is well known, the non-Gaussianity parameter fNL, which is often used to characterize the amplitude of the scalar bi-spectrum, can be expressed completely in terms of the scalar spectral index ns in the squeezed limit, a relation that is referred to as the consistency condition. This relation, while it is largely discussed in the context of slow roll inflation, is actually expected to hold in any single field model of inflation, irrespective of the dynamics of the underlying model, provided inflation occurs on the attractor at late times. In this work, we explicitly examine the validity of the consistency relation, analytically as well as numerically, away from slow roll. Analytically, we first arrive at the relation in the simple case of power law inflation. We also consider the non-trivial example of the Starobinsky model involving a linear potential with a sudden change in its slope (which leads to a brief period of fast roll), and establish the condition completely analytically. We then numerically examine the validity of the consistency relation in three inflationary models that lead to the following features in the scalar power spectrum due to departures from slow roll: (i) a sharp cut off at large scales, (ii) a burst of oscillations over an intermediate range of scales, and (iii) small, but repeated, modulations extending over a wide range of scales. It is important to note that it is exactly such spectra that have been found to lead to an improved fit to the CMB data, when compared to the more standard power law primordial spectra, by the Planck team. We evaluate the scalar bi-spectrum for an arbitrary triangular configuration of the wavenumbers in these inflationary models and explicitly illustrate that, in the squeezed limit, the consistency condition is indeed satisfied even in situations consisting of strong deviations from slow roll. We conclude with a brief discussion of the results.

How Effective are Investment Subsidies in Flanders? An RDD Approach

This paper analyzes the effects of a subsidy program for small and medium sized enterprises in Flanders from 2004 to 2009 (the program was called 'growth grant', or in Dutch 'de groeipremie'). The subsidies were awarded according to a ranking system that favored young, growing and productive firms with a strong cash flow, granting subsidies to the highest scoring firms until the depletion of funds. The nature of this allocation system creates a sharp cut off in granting the subsidy according to the score: only firms above the cut off score are granted the subsidy. This quasi-experimental setting allows us to estimate a local average treatment effect around this cut off, making use of regression discontinuity design (RDD) methodologies. We find a sizable positive effect on firm-level investment, employment, output and productivity for the firms that were granted the subsidy, but mainly for the very small firms, e.g. firms with less than 10 employees. For the larger firms, we only find a positive effect on profits, which suggests that they use the subsidy to finance investments that they would have undertaken anyway.

Removal of active-fixation coronary sinus leads using a mechanical rotation extraction device.

Active fixation coronary sinus (CS) leads are widely used in cardiac resynchronization therapy (CRT). Due to their low dislodgement rates they are an attractive option for implanters. However, extraction of active fixation leads is a complex procedure that bears potential fatal risks for patients. We analyzed all patients undergoing StarFix® (Medtronic Inc., Minneapolis, MN, USA) extraction because of severe infection at our institution. Indication for extraction was severe device infection. Procedural outcomes as well as patient characteristics are reported. For removal of the leads a 9-Fr Evolution® (Cook Intravascular Inc., Leechburg, PA, USA) mechanical rotation extraction sheath was used. Between 2011 and 2014, six patients underwent extraction of StarFix® leads. One patient was female, whereas the others were males (mean age 64 ± 12 years). Implant duration was 46.5 ± 8.2 months before removal. All leads could be successfully extracted totally with the Evolution®. In one patient (16.6%) pericardial tamponade occurred immediately requiring surgical intervention. After establishment of cardiopulmonary bypass a 5-mm sharp cut in the lateral vein of the CS could be identified. It was fixed and the patient survived. On all leads, significant tissue growth between the fixation lobes could be observed. As illustrated by our cases, Attain StarFix® leads implanted years ago can be extracted with the help of a mechanical extraction sheath. However, this procedure bears potential risks and should only be performed with a cardiac surgery standby. If clinicians evaluate the implantation of Attain StarFix® leads in patients who are young or at high risk for device infection, they should be aware of these findings.

Comments: The Problem of Water

Editor's column The issue of water needs for shale resource development has largely focused on public concern about possible constraints on water supplies, particularly in areas suffering from drought. A new study suggests that without technological breakthroughs or changes in how the oil and gas industry manage water, development of shale production could be hampered in areas with the largest estimated reserves. Some cities in the United States suffering from drought have imposed bans on hydraulic fracturing, even though oil and gas industry water use compares favorably with that of other industries (see Beyond the Headlines, July 2014 JPT, p. 20). The new report issued by the World Resources Institute, titled “Global Shale Development: Water Availability and Business Risk,” focuses not on public concerns, but energy company risk instead. It contends that water-availability challenges could limit shale resource development on six continents, including in areas with some of the greatest potential for shale production. The report’s executive summary looks at three countries in particular and assesses the potential water challenges. China. The world’s largest energy producer and consumer also has the world’s largest technically recoverable shale gas resources, according to estimates from the US Energy Information Administration (see table, p. 86). But most of these resources are located in areas of “highest water stress,” according to the study. More than 60% of the resources are in areas with arid conditions or highbaseline water stress. Although Chinese oil companies recently have increased expenditures for shale development, the Chinese government in August cut in half its 2020 shale gas target after several years of disappointing E&amp;P efforts. Argentina. Approximately 28% of this country’s shale gas resources, the world’s second-largest according to the EIA, are located in arid areas. Argentina has also had production success, with the joint venture between Chevron and YPF more than tripling production in the Neuquen basin shale formation known as Vaca Muerta from last year. United Kingdom. Public concern about hydraulic fracturing runs high, but the government recently began offering tax incentives to jump-start shale development. Given the high industry and public demand for water, the report classifies a third of the UK’s shale resources in the high to extremely high water stress category. The institute’s mission is concerned more with the environment than with energy development and production, but its warnings are not considerably different from other recent studies, such as one done by consultants Wood Mackenzie last year titled “Troubled Waters Ahead?” It noted that although agriculture uses two-thirds of global freshwater supplies, energy is by far the largest industrial user (more than 15%). The United Nations is predicting a 40% decrease in freshwater supplies by 2030, which will put additional focus on the amount of water used by oil and gas concerns. The solution may lie in technology development and better water management. Already the industry has made strides in water reuse and recycling, such as in the Permian Basin, an area facing extreme drought conditions (see p. 68). Numerous research projects are under way throughout the industry that could result in sharp cuts in demand for fresh water or the elimination of fresh water use within a few years. JPT

The influence of water jet diameter and bone structural properties on the efficiency of pure water jet drilling in porcine bone

Abstract. Using water jets in orthopedic surgery to drill holes in bones can be beneficial due to the absence of thermal damage and the always sharp cut. To minimize operating time and the volume of water that is used, the efficiency (volume of removed bone per added volume of water) of the water jet should be maximized. The goal was to study the effect of the open trabecular bone structure on the efficiency for different water jet diameters. 86 holes were drilled in porcine tali and femora submerged in water with nozzles of 0.3, 0.4, 0.5 and 0.6 mm at 70 MPa during 5 s and a standoff distance of 8 mm. MicroCT scans were made to measure the removed bone volume and the bone structural properties Trabecular Spacing (Tb.Sp.), Trabecular Thickness (Tb.Sp.) and Bone Volume Fraction (BV/TV). Pearson's correlation tests (p &lt; 0.05, 95% confidence interval) were performed for each water jet diameter using the bone structural property as an independent factor and the efficiency as a dependent factor. No significant differences were found between the nozzle diameters in the material removal rates per added volume of water. The efficiency decreased for an increase in Tb.Th. and BV/TV for nozzles of 0.3, 0.4 and 0.5 mm. The 0.6 mm nozzle showed less influence of the Tb.Th. and BV/TV. The Tb.Sp. has no influence on the efficiency of a water jet. The total volume of added water combined with the Tb.Th. or BV/TV is a leading measure for the volume of bone material that is removed, which provides freedom in the development of water jet instruments as the nozzle diameter, pressure and jet time can be chosen in accordance to the maximum operating time requirements or dimensional limitations of a design.

Formal Proof of Flowers & Ruderman's Instability Mechanism in Magnetic Stars

In 1977, Flowers and Ruderman described a perturbation that destabilized a purely dipolar magnetic field in a star. They considered the effect of cutting the star in half along a plane parallel to the symmetry axis and rotating each half 90 degrees in opposite directions, which would cause the energy of the magnetic field in the exterior of the star to be greatly reduced, just as it happens with a pair of aligned magnets. We formally solve for the energy of the external magnetic field and check that it decreases monotonously along the entire rotation.We also describe the instability using perturbation theory, and see that it happens due to the work done by the interaction of the magnetic field with surface currents.Finally, we consider the stabilizing effect of adding a toroidal field by studying the internal energy perturbation when the rotation is not done along a sharp cut, but with a continuous displacement field that switches the direction of rotation across a region of small but finite width. Using these results, we estimate the relative strengths of the toroidal and poloidal field needed to make the star stable to this displacement and see that the energy of the toroidal field required for this is much smaller than the energy of the poloidal field.