Excess Slack Research Articles

Permanent deformation of triangle weaver silk enables ultrafast tangle-free release of spider webs.

Entanglements are common in both natural and artificial systems and can result in both beneficial and harmful effects. Most spider webs are static structures held under constant tension and do not tangle. However, many spiders actively load tension into their webs by coiling silk threads that are released to "fire" webs at prey. Here we test whether or not tangling occurs during the rapid release of webs built by the triangle spider Hyptiotes cavatus. We use high-speed videography to examine the release of the spider's web, looking for signs of tangling both visually on the videos and on acceleration graphs. The spider tenses the web by pulling on a silken anchor line using a leg-over-leg movement, deforming the silk into permanent coils and storing excess slack in a loose bundle between the spider's legs. This 1-3cm long bundle of coils straightens during the web's release in as few as 4ms. Though the messy silk coils are pressed closely together, the web's release is never impeded by catastrophic tangling. This lack of serious tangling is perhaps due to the permanent coils preventing random movement of the silk. The coils also compact the loose silk, preventing interference with the spider's movement. The ability to coil its anchor line allows H. cavatus to permanently restructure its silk, facilitating its active web-hunting behavior. Our findings broaden our knowledge of silk manipulation by spiders and may give insights into creating tangle-free systems through structural changes.

When is discretionary fiscal policy effective?

Abstract We investigate the effects of discretionary changes in government spending and taxes using a medium-scale nonlinear vector autoregressive model with policy shocks identified via sign restrictions. Tax cuts and spending increases have larger stimulative effects when there is excess slack in the economy, while they are much less effective, especially in the case of government spending increases, when the economy is close to potential. We find that contractionary shocks have larger effects than expansionary shocks across the business cycle, but this is much more pronounced during deep recessions and sluggish recoveries than in robust expansions. Notably, tax increases are highly contractionary and largely self-defeating in reducing the debt-to-GDP ratio when the economy is in a deep recession. The effectiveness of discretionary government spending, including its state dependence, appears to be almost entirely due to the response of consumption. The responses of both consumption and investment to discretionary tax changes are state dependent, but investment plays the larger quantitative role.

A New Cost-Aware Sensitivity-Driven Algorithm for the Design of FIR Filters

Design for low complexity FIR filters has been an area of intensive research over the last two decades. Recent approaches to integrating common subexpression elimination with filter coefficient synthesis are based on single-minded reliance on bit width truncation or common subexpression sharing to fulfill the frequency response specifications. Such biases have a strong tendency to overfit or underfit the response prematurely, and increase the implementation cost. In this paper, a new algorithm is proposed to synthesize finite-precision coefficients with low implementation cost from the frequency response specifications of linear phase FIR filter. Overfitting is overcome by admitting the most sensitive subexpressions followed by isolated nonzero digits according to their sensitivities to the change in frequency response error if they are independently removed. To leverage on adder reuse of common subexpressions, common subexpressions of each length are admitted into the coefficients immediately after their most sensitive member. Trivial nonzero digits piggybacked on the admission of common subexpression are pruned to remove the excess slack from the finally selected least cost finite-precision coefficient set. To avoid underfitting, the filter length and word length of coefficients are not fixed but determined by how much incremental slack in the frequency response can be harvested from each additional tap and expanded bit. The effectiveness of the proposed algorithm in designing low power and area-efficient FIR filters is demonstrated by comparing its logic synthesis and power simulation results with other FIR filter coefficient synthesis algorithms. On average, the proposed algorithm saves about 20.9% to 72.7% of area and power consumptions on various sizes of benchmark FIR filters, and improves the area and power efficiency of a filter bank designed for feature extraction of EEG signals by 33.9% to 54.8% over the competing algorithms.

When Do Discretionary Changes in Government Spending or Taxes Have Larger Effects?

We investigate the effects of discretionary changes in government spending and taxes using a medium-scale nonlinear vector autoregressive model with policy shocks identified via sign restrictions. Tax cuts and spending increases have larger stimulative effects when there is excess slack in the economy, while they are much less effective, especially in the case of government spending increases, when the economy is close to potential. We find that contractionary shocks have larger effects than expansionary shocks across the business cycle, but this is much more pronounced during deep recessions and sluggish recoveries than in robust expansions. Notably, tax increases are highly contractionary and largely self-defeating in reducing the debt-to-GDP ratio when the economy is in a deep recession. The effectiveness of discretionary government spending, including its state dependence, appears to be almost entirely due to the response of consumption. The responses of both consumption and investment to discretionary tax changes are state dependent, but investment plays the larger quantitative role.

Confidence–Competence Mismatch and Reasons for Failure of Non-Medical Tourniquet Users

Objective: Tourniquet application is a lifesaving skill taught worldwide in first aid bleeding control courses. We observed performance among non-medical users of tourniquets in their confidence, competence, and reasons for failure. Methods: 179 Israeli military recruits without prior medical training underwent their standard first aid course where they learned Combat Application Tourniquet (CAT; Composite Resources, Rock Hill, SC, USA) use. After course completion, they self-reported confidence in tourniquet use. User performance was assessed 7–14 days later using a HapMed™ mannequin that assessed time, pressure, and blood loss. Competent performance required in aggregate: 1) use with pressure of 200 mmHg or more, 2) hemorrhage volume of less than 638 mL, and 3) correct placement of the tourniquet. For failed performance, a reason for failure was reported independently by both the user and an expert observer. Results: 45 of 179 user performances (25%) were competent. Users who reported high confidence had only a slightly higher chance of achieving competence in tourniquet application (r = 0.17, p = 0.022). The most common reason for failure was excess slack in the CAT's strap (experts 55%, users 39%), and too few turns of the windlass (23% and 31%, respectively) was the second most common reason. Expert and user evaluations had poor agreement (κ = 0.44, 95% CI 0.32–0.56). Conclusion: The most common reason for failed use of tourniquets among non-medical users was excess slack in the tourniquet strap. Users self-evaluated their performance inaccurately and demonstrated a confidence-competence mismatch. These pitfalls in performance may help tourniquet instructors improve training of caregivers.

Letter to the Editor: Marino et al. Inappropriate mode switching clarified by using a chest radiograph

To the Editor, I read with great interest the article by Marino et al. entitled “Inappropriate mode switching clarified by using a chest radiograph.” [1]. The authors have explained a case of dual-chamber pacemaker malfunction, caused by intermittent high-frequency noises. They claimed that this happened because of lead–lead interaction caused by excess slack of atrial and ventricular leads. In this case report, the authors did not explain the pacemaker parameters, such as the programmed lead sensation polarity (unipolar or bipolar), intrinsic R wave amplitude, and ventricular sensing threshold. With a close attention to the atrial and ventricular electrograms, it is clear that the noise is seen in both electrograms. The authors claimed that the noise is more prominent in the atrial channel than in the ventricular channel. However, this higher level of the noise in the atrial electrogram is due to automated gain, which increased the gain in the atrial channel. Thus, with the same gains, it seems that the noise amplitude will be the same, and changes in the amplitude in both the electrograms will be comparable at each moment. Replacement of the baseline with high-frequency signals, its simultaneity in both farfield electrograms, and no constant relation to the cardiac cycle are compatible with extra cardiac electromagnet interference. Myopotential oversensing is also presented with high-frequency noise, especially in widely spaced electrodes or unipolar electrograms, and can hence cause device malfunction, particularly when the sensing polarity is programed as unipolar. The effect of this interference may differ between atrial and ventricular electrograms, according to the distance from the sensing field of the electrodes. For excluding this possibility, it is better to look at the bipolar electrograms (recorded from closely spaced electrodes). Finally, as the authors have mentioned, some other possibilities, such as lead-connector problems, may present intermittently; however, the noise often saturates the amplifier range. Changes in the impedance may be documented during pocket manipulation [2]. Therefore, I recommend that the authors recheck the device settings such as sensing polarities and look for external electromagnetic interferences, as this is the most probable cause.

Taxis as a Recourse Option for Ridesharing Services

Ridesharing services commonly offered at airports and to mobility-impaired persons exist worldwide. Unlike operators in conventional public transit, ridesharing operators maintain flexible routes and schedules that are used in providing door-to-door service. These routes and schedules are typically created by using the assumption of perfect foresight about future travel times. In practice, however, vehicles may encounter traffic congestion, be delayed because of road work or an accident, or even break down. Thus, the routes and schedules may adhere to quality-of-service constraints in planning when perfect conditions are assumed, but operationally they often violate such constraints. This paper investigates the effectiveness of routes and schedules created under a deterministic travel time assumption. The paper evaluates practical solutions that force the schedules to include excess slack. Finally, the paper proposes and assesses a recourse option for use in actual operations of assigning to taxis those passengers who are likely to be picked up late. The evaluation was completed on a real-world case study in Richmond, Virginia.

Embracing the Second Best?Synchronization of Reforms Rhythms, Slack, and Firm Performance

We analyze the understudied impact of synchronization of reforms rhythms on the performance of transition economy firms. We argue that higher synchronization of reforms rhythms improves the firms’ performance due to timing synergies among the different reforms types. Additionally, we propose that excess high-discretion slack further strengthens the performance benefits from a higher synchronization of reforms rhythms because it allows the transition economy firms to more quickly adapt to their changing institutional environment. Thus, we extend the institution-based view of the firm by shifting its traditional focus on institutional differences across countries to a new research direction that accounts explicitly for the timing of implementation—concurrent or sequential—of the different types of reforms rhythms within a country over time. Our test on a sample of 430 firms from 13 transition economies during 1991-2009 supports our arguments.

Pacemaker Lead Prolapse through the Pulmonary Valve in Children

Transvenous pacemaker leads in children are often placed with redundant lead length to allow for anticipated patient growth. This excess lead may rarely prolapse into the pulmonary artery and potentially interfere with valve function. We sought to determine the response to lead repositioning on pulmonary valve insufficiency. Retrospective reviews of demographics, lead type, implant duration, and radiography and echocardiography. A total of 11 pediatric patients were identified with lead prolapse through the pulmonary valve, of which nine patients underwent procedures to retract and reposition the lead (age at implant 9 +/- 4 years, age at revision 13 +/- 4 years). The implant duration prior to revision was 4 +/- 3 years. Two leads required radiofrequency extraction sheaths for removal, two pulled back using a snare, while five leads were simply retracted and repositioned. Tricuspid regurgitation was none/trivial (three), mild (four), or moderate (two) and only two improved with repositioning or replacement. Pulmonary regurgitation preoperatively was mild (three), mild-moderate (two), or moderate (four) compared with trivial (three), mild (four), and moderate (two) after revision. Patients with longer-term implanted leads had less improvement in pulmonary insufficiency. Two patients had mild pulmonary stenosis from lead-related obstruction. Prolapse of transvenous pacing leads into the pulmonary artery can occur when excess slack is left for growth. Leads can often be repositioned, but may require extraction and replacement, particularly if chronically implanted and adherent to valve apparatus. Lead revision does not always resolve pulmonary insufficiency, potentially leaving permanent valve damage.

Manufacturing firm reaction to supplier failure and recovery

PurposeManufacturing firm reaction to a supply failure is important because buyer dissatisfaction may induce related development or switching costs. The purpose of this paper is to ask: what is the impact of a supply failure and recovery on manufacturing firm dissatisfaction with the supplier?Design/methodology/approachA case study approach is used based on interviews of key informants, examining four US manufacturers classified by industry type (aerospace and electronics) and firm size (large and small).FindingsManufacturing firm dissatisfaction increases relative to the accumulated impact of the supply failure, and is reduced when the manufacturer has slack to absorb the failure or shares blame for it. The supplier's failure recovery reduces dissatisfaction to the extent that it demonstrates the supplier's long‐term commitment to the relationship. The findings indicate that attributes of the failure, the failure recovery, and context must be taken into account when considering how a supplier's recovery may ameliorate the negative impact of a supply failure.Research limitations/implicationsThe results are constrained by the number of cases we collected and by the limitations of retrospective interviews.Practical implicationsThe findings suggest that manufacturers can over‐react to a failure because of the perceptual nature of risk, or under‐react to a failure because of excess slack or switching costs.Originality/valueThis paper adds significant detail to our understanding of how supplier failure and recovery impact a manufacturer's dissatisfaction with a supplier, the antecedent to costs involved with supplier development or switching.

Flattening the Organization: The Effect of Organizational Reporting Structure on Budgeting Effectiveness

This study investigates whether increasing a superior's span of control reduces the effectiveness of capital budgeting in eliciting truthful reports. We conduct an experiment based on a modification of the capital budgeting setting described by Antle and Eppen (1985). This modification incorporates the notion that the superior's utility for wealth increases at a decreasing rate, as well as the recent empirical evidence that individuals have utility for enforcing social norms. Specifically, we assume the superior is willing to incur a cost in order to punish a subordinate who she believes is incorporating excess slack in his budget, thereby violating a social norm. These theoretical refinements lead to the prediction that as the span of control increases, superiors will be more willing to reject project proposals with high budgeted costs. We further predict that subordinates under an expanded span of control will anticipate the superiors' increased toughness, and will respond by reducing their budgetary slack. We conduct an experiment to test these predictions. The experimental results are consistent with our theory. That is, as the span of control is increased, superiors show a greater willingness to reject projects for which they believe slack is excessive, and subordinates respond by reducing slack. The net result of these two effects is that as the span of control is increased, superiors earn more profit per subordinate. Thus, our study suggests that increasing the span of control can improve the effectiveness of the budgeting process, which is an important component of most firms' control environments. Although prior research has generally assumed that increasing the span of control weakens the control environment, our study demonstrates that increasing the span of control can actually strengthen it.

NCAP Test Improvements with Pretensioners and Load Limiters

New Car Assessment Program (NCAP) test scores, measured by the United States Department of Transportation's (USDOT) National Highway Traffic Safety Administration (NHTSA), were analyzed in order to assess the benefits of equipping safety belt systems with pretensioners and load limiters. Safety belt pretensioners retract the safety belt almost instantly in a crash to remove excess slack. They tie the occupant to the vehicle's deceleration early during the crash, reducing the peak load experienced by the occupant. Load limiters and other energy management systems allow safety belts to yield in a crash, preventing the shoulder belt from directing too much energy on the chest of the occupant. In NCAP tests, vehicles are crashed into a fixed barrier at 35 mph. During the test, instruments measure the accelerations of the head and chest, as well as the force on the legs of anthropomorphic dummies secured in the vehicle by safety belts. NCAP data from model year 1998 through 2001 cars and light trucks were examined. The combination of pretensioners and load limiters is estimated to reduce Head Injury Criterion (HIC) by 232, chest acceleration by an average of 6.6 g's, and chest deflection (displacement) by 10.6 mm, for drivers and right front passengers. The unit used to measure chest acceleration (g) is defined as a unit of force equal to the force exerted by gravity. All of these reductions are statistically significant. When looked at individually, pretensioners are more effective in reducing HIC scores for both drivers and right front passengers, as well as chest acceleration and chest deflection scores for drivers. Load limiters show greater reductions in chest acceleration and chest deflection scores for right front passengers. By contrast, in make-models for which neither load limiters nor pretensioners have been added, there is little change during 1998 to 2001 in HIC, chest acceleration, or chest deflection values in NCAP tests.

The tightrope to e-business project success

Even though U.S. businesses spend half of their business equipment budgets on IT, only one out of six software projects is successful. Annually, this adds up to about $75 billion a year in failed projects, $22 billion in cost overruns, and another $175 million for systems that deliver less than they claim [9]. The elusivity of success is rooted in organizations’ inability to manage—or even recognize—the unexpected. Inattention to the emergent gap between what’s delivered and what’s finally needed, not technical incompetence, is what stumps even the best of intentions. Code, however good, cannot compensate for poor conceptualization. A new philosophy that views software as a medium in which knowledge is embedded rather than a product is emerging in some circles of the software community [2, 8]. Proponents of this view encourage embedding accurate knowledge into the design of a system over trying to manage requirements. Software project execution is like walking a tightrope from idea to implementation. It takes just the right balance between methodology and imagination, and following rules and knowing when to break them. Either excess slack or inflexibility guarantee a fall. We conducted a field study to assess the merits of this view and determine whether embedding knowledge in software design influences how well a project adapts to changing technology, unstable business needs, and customers who cannot seem to make up their mind. We found strong support for this emerging perspective: project teams that excel at knowledge integration best manage the unexpected to successfully execute innovation-intensive software projects. This article discusses the implications of our findings for software practice. From Engineering Imagination to Imagination Engineering The most difficult part of building a new system is determining what to build. Determining that is clearly a process of reducing ignorance about customer needs, technology, and a project’s business context [3]. A system is the byproduct of such knowledge. When that knowledge itself is incomplete, a project is built on an architecture of misunderstood business needs.

Do Broad Scope Managerial Accounting Systems Moderate the Effects of Budget Emphasis, Budget Participation and Perceived Environmental Uncertainty on the Propensity to Create Budgetary Slack?

This study empirically investigates the potential moderating effect of broad scope managerial accounting system use on several variables previously shown to contribute to the formation of budgetary slack. It is hypothesized that the additional information provided via a broad scope managerial accounting system would reduce uncertainty for managers and eliminate a portion of the need to build excess slack into the budget. Survey data collected from Fortune 1000 managers indicates that the use of broad scope managerial accounting systems does not moderate the impact of budget emphasis, budget participation and perceived environmental uncertainty on the propensity to create budget slack.

RESEARCH NOTE: Shoulder Belt Use and Effectiveness in Cars with and without Window Shade Slack Devices

Using National Acccident Sampling System files for the calendar years 1982-1986, shoulder belt use and effectiveness were compared among 1974-1980 model year cars with and without window shade devices, which human factors research has found to produce excess slack in the belts. Although shoulder belt use was not correlated to presence or absence of the window shade mechanism when model year and calendar year effects were controlled statistically, the effectiveness of belts in cars with the window shade device was consistently less than in cars without the device, particularly so in larger vehicles.

Migration of epicardial pacemaker leads

The implantation of permanent pacemakers often gives rise to complications. Migration of leads, an unusual complication, occurred in two of our patients with epicardial pacemakers. In one case lead fracture and sussequent displacement due to heart action occurred after an automobile accident. In the second case looping and migration of the wire occurred within a day after implantation although the lead continued to function properly for six months. The probable cause of migration in this patient was excess slack.

A statistical reliability approach to linear programming

The implications of the probabilistic interpretation of a linear programming system in terms of the statistical theory of reliability are here analyzed. The concept of reliability, its relation to the presence of excess resources or organizational slack and to the age distribution of specific resources like capital with a specific depletion function is explored from an economic viewpoint. Possible uses of this reliability approach for economic models of resource allocation are also indicated, particularly for the case when the optimal durability of fixed resources is to be determined.