Lack Of Repeatability Research Articles

Modern statistical and philosophical framework for uncertainty assessment in biometric performance testing

The question of estimating uncertainty in measurement is fundamental to all scientific fields. In the field of automated human recognition, lack of repeatability and reproducibility of measurements has been noted since at least the 1970s. This study discusses current approaches to estimation of measurement uncertainty within the broader context of scientific philosophy and measurement science. The authors discuss the Duhem–Quine thesis on testing holism and international standards on estimating and reporting uncertainty in laboratory measurements, then apply these concepts to the estimation of uncertainty in technology, scenario and operational testing in biometrics. The authors advocate for moving beyond the calculation of ‘coverage’ intervals as defined in the ISO/IEC ‘guidelines for the expression of uncertainty in measurement’ to full application of the concepts of uncertainty assessment.

Impulse source versus dodecahedral loudspeaker for measuring parameters derived from the impulse response in room acoustics

This study investigates the performance of dodecahedral and impulse sources when measuring acoustic parameters in enclosures according to ISO 3382-1 [Acoustics-Measurement of room acoustic parameters. Part 1: Performance spaces (International Organization for Standardization, Geneva, Switzerland, 2009)]. In general, methods using speakers as a sound source are limited by their frequency response and directivity. On the other hand, getting impulse responses from impulse sources typically involves a lack of repeatability, and it is usually necessary to average several measurements for each position. Through experiments in different auditoriums that recreate typical situations in which the measurement standard is applied, it is found that using impulse sources leads to greater variation in the results, especially at low frequencies. However, this prevents subsequent dispersions due to variables that this technique does not require, such as the orientation of the emitting source. These dispersions may be relevant at high frequencies exceeding the established tolerance criteria for certain parameters. Finally, a new descriptor for dodecahedral sources reflecting the influence their lack of omnidirectionality produces on measuring acoustic parameters is proposed.

Influence of the freezing method on the changes that occur in grape samples after frozen storage

Sample freezing is frequently used in oenological laboratories as a compromise solution to increase the number of samples that can be analysed, despite the fact that some grape characteristics are known to change after frozen storage. However, freezing is usually performed using standard freezers, which provide a slow freezing. The aim of this work was to evaluate whether blast freezing would decrease the impact of standard freezing on grape composition. Grape quality parameters were assessed in fresh and in frozen stored samples that had been frozen using three different procedures: standard freezing and blast freezing using either a blast freezer or an ultra-freezer. The implications of frozen storage in grape samples reported in earlier research were observed for the three freezing methods evaluated. Although blast freezing improved repeatability for the most problematic parameters (tartaric acidity, TarA; total phenolics, TP), the improvement was not important from a practical point of view. However, TarA and TP were relatively repeatable among the three freezing procedures, which suggests that freezing had an effect on these parameters independently of the method used . According to our results, the salification potential of the must is probably implied in the changes observed for TarA, whereas for TP the precipitation of protoanthocyanins after association with cell wall material is hypothesized to cause the lack of repeatability between fresh and frozen grapes. Blast freezing would not imply a great improvement if implemented in oenological laboratories, at least for the parameters included in this study.

Adhesion and Friction Coupling in Atomic Force Microscope-Based Nanopushing

The use of the atomic force microscope (AFM) as a tool to manipulate matter at the nanoscale has received a large amount of research interest in the last decade. Experimental and theoretical investigations have showed that the AFM cantilever can be used to push, cut, or pull nanosamples. However, AFM-based nanomanipulation suffers a lack of repeatability and controllability because of the complex mechanics in tip-sample interactions and the limitations in AFM visual sensing capabilities. In this paper, we will investigate the effects of the tip-sample interactions on nanopushing manipulation. We propose the use of an interaction model based on the Maugis–Dugdale contact mechanics. The efficacy of the proposed model to reproduce experimental observations is demonstrated via numerical simulations. In addition, the coupling between adhesion and friction at the nanoscale is analyzed.

Significant enrichment of Y‐bearing chromosome human spermatozoa using a modified centrifugation technique

The effective separation of X- and Y-bearing chromosome spermatozoa has been a topic of major attraction to a number of scientific disciplines. Approaches have typically been based upon either the kinetic or the physical characteristics of spermatozoa. Much of the information available to date has either suggested conflicting evidence between different approaches or a lack of repeatability, while other robust and reproducible techniques require expensive equipment and are being questioned with relation to their safety in clinical applications. This study describes a safe and efficient method for the successful enrichment of the Y-bearing chromosome spermatozoa cells from their X counterparts in the human male using a simple approach based on centrifugation. Five donor candidates with normal semen profiles and proven fertility were recruited. In total, 20 semen specimens were processed using conventional swim-up. During each attempt, half of the swim-up product was subjected to the enrichment technique and the other half served as control. Parameters important for successfully skewing sex ratios included the relative centrifugal force, the duration of centrifugal separation and the number of centrifugation rounds. Assessment of samples following the separation technique was effected by a three-colour-labelled fluorescent in situ hybridization. More than 1000 spermatozoa for each donor specimen were assessed for the presence of an X or Y chromosome. The enrichment technique produced a significantly higher (p < 0.001) overall frequency of 85.5% for the Y-bearing chromosome spermatozoa in the experimental group (3606 X-bearing/21, 209 Y-bearing) compared with a frequency of 50.1% in the control group (11,801 X-bearing/11,269 Y-bearing), where there was no statistically significant difference in the number of either X- or Y-chromosome-bearing spermatozoa. In conclusion, successful skewing of human Y-bearing chromosome spermatozoa can be reproducibly achieved by the use of simple swim-up followed by a meticulous centrifugation protocol.

Development of a Synthetic Skin Simulant Platform for the Investigation of Dermal Blistering Mechanics

Excessive frictional loading to the skin often results in the formation of blisters, due to the transmission of shear loading to the interfaces between dermal cell strata. The consequences of blistering range from mild discomfort to serious infection. In some patients, such as those disposed to epidermolysis bullosa or neuropathic diabetes, blisters can severely degrade life quality. Investigation of environmental and application parameters that affect blister formation has occurred primarily as a qualitative, observational pursuit on human subjects, which has often led to confounding of data and lack of repeatability. The authors have developed a Synthetic Skin Simulant Platform (3SP) that reproduces the mechanical behavior of human skin when exposed to tribological loading. The platform is an assembled construct of bonded elastomeric layers that act as surrogates for the epidermis, basement membrane, dermis, and subdermal structure. Epidermal (top layer) materials are typically silicone or polyurethane films with a friction coefficient akin to human skin, while sublayers display mechanical properties similar to their anatomical analogs. Blistering is evident optically by examining the separation voids formed after applying shear loads to the epidermal layer. The 3SP has been used in a two-axis pin-on-flat tribometer with a stainless steel indenter to study the normal load and friction coefficients encountered at the onset of frictional blistering. The 3SP allows for modulation of friction coefficient, interfacial adhesion strength, and subdermal stiffness for investigation of blistering damage to various anatomical sites. Experimental results have been compared to human test data and have shown that the 3SP provides the potential to make significant advances with respect to skin tribology research.

Development of a Simple Mechanical Impact System as a Non-Explosive Seismic Source

A Simple Mechanical Impact System (SMIS) was developed recently as a non-explosive seismic source. The SMIS consists of an impact head, a steel rod with extensions, and an anchoring system. The system is small and simple, and can be conveniently installed in a shallow borehole oriented in any direction. The SMIS was developed to address two problems commonly associated with non-explosive seismic sources: insufficient seismic strength and lack of repeatability. Field tests have shown that it is possible to produce clear and repeatable signals with this system even when the SMIS is installed in a coal seam.

Factors affecting porcine sperm mediated gene transfer

“Sperm mediated gene transfer” (SMGT) is based on the ability of sperm cells to bind exogenous DNA. The main objective of this study was to improve the production of transgenic pigs by SMGT. Taking into account that there is a lack of repeatability in studies of SMGT and that the mechanism of binding and internalization of exogenous DNA is a question that has not been solved, different factors involved in the production of transgenic animals by SMGT method were evaluated. Here we set out to: (1) evaluate the sperm capacity to bind exogenous DNA after DMSO treatment; (2) determine the location of the transgene–spermatozoa interaction; and (3) evaluate the efficiency of production of transgenic piglets by deep intrauterine artificial insemination (AI) with sperm incubated with DNA. The percentage of DNA binding was higher than 30% after 2 h of co-culture, but it was not affected by sperm treatment with DMSO (0.3% or 3%). The integrity of the sperm plasma membrane plays a critical role in DNA interaction, and altered plasma membranes facilitate interactions with exogenous DNA. DNA bound mainly to spermatozoa with reduced viability. DNA molecules were found to be mainly associated to the post-acrosomal region (61.9%). After deep intrauterine AI a total of 29 piglets were obtained, but none of them integrated the transgene. In conclusion, although it has been confirmed that DNA can associate with boar spermatozoa, the efficiency of producing transgenic pigs by AI was not confirmed by the present experiments, mainly due to a reduced DNA binding to functional spermatozoa.

Seasonal variation in colony size of Brazilian free-tailed bats at Carlsbad Cavern based on thermal imaging

The colony of Brazilian free-tailed bats (Tadarida brasiliensis) at Carlsbad Cavern, New Mexico, is a wellknown example of this highly gregarious and conspicuous species in North America. For nearly a century researchers have tried to estimate the size of this colony, but different census methods and lack of repeatability have resulted in questionable estimates that have given rise to poorly understood but highly popularized, longterm population trends for this migratory species. In this study we present accurate seasonal estimates of colony size based on a recently developed census method—thermal infrared imaging and computer vision analysis. The size of the colony was estimated several times monthly from March through October 2005. Our estimates range from 67,602 to 793,838 bats, values that are orders of magnitude lower than the largest historic estimates. Consecutive estimates of nightly emergences show fluctuations of as many as 291,000 individuals, indicating that colony composition is considerably more dynamic than previously thought. Our results, combined with a quantitative analysis of emergence behavior, question the validity of early historic estimates that millions of bats once roosted in this cave and suggest that the long-term pattern of decline reported for this species might not be as severe as currently thought. DOI: 10.1644/08-MAMM-A-391R.1.

Two hardware-based approaches for deterministic multiprocessor replay

Modern computer systems are inherently nondeterministic due to a variety of events that occur during an execution, including I/O, interrupts, and DMA fills. The lack of repeatability that arises from this nondeterminism can make it difficult to develop and maintain correct software. Furthermore, it is likely that the impact of nondeterminism will only increase in the coming years, as commodity systems are now shared-memory multiprocessors. Such systems are not only impacted by the sources of nondeterminism in uniprocessors, but also by the outcome of memory races among concurrent threads. In an effort to help ease the pain of developing software in a nondeterministic environment, researchers have proposed adding deterministic replay capabilities to computer systems. A system with a deterministic replay capability can record sufficient information during an execution to enable a replayer to (later) create an equivalent execution despite the inherent sources of nondeterminism that exist. With the ability to replay an execution verbatim, many new applications may be possible: Debugging: Deterministic replay could be used to provide the illusion of a time-travel debugger that has the ability to selectively execute both forward and backward in time. Security: Deterministic replay could also be used to enhance the security of software by providing the means for an in-depth analysis of an attack, hopefully leading to rapid patch deployment and a reduction in the economic impact of new threats. Fault Tolerance: With the ability to replay an execution, it may also be possible to develop hot-standby systems for critical service providers using commodity hardware. A virtual machine (VM) could, for example, be fed, in real time, the replay log of a primary server running on a physically separate machine. The standby VM could use the replay log to mimic the primary's execution, so that in the event that the primary fails, the backup can take over operation with almost zero downtime.

Repeatability of Female Reproductive Traits in Pigmy Rattlesnakes (Sistrurus miliarius)

The consistency of a trait's expression within individuals reflects both its maximal possible heritability and that trait's susceptibility to the influence of temporal variation in environmental conditions. A lack of repeatability in reproductive traits may also result if there are ontogenetic changes in female reproductive effort. In a decade-long study, we collected data on the reproductive traits (including female SVL, female postpartum condition, litter size, total litter mass, mean offspring mass, and birth date) of free-ranging Pigmy Rattlesnakes in central Florida. We captured and held the study snakes in field enclosures for several weeks before parturition each year. A total of 24 females produced two or more litters during the course of the study. We determined the repeatability for each reproductive trait. Our results indicated that four of the six reproductive traits had high and statistically significant repeatability despite annual variation in environmental conditions. A lack of growth in adult Sistrurus miliarius and the ability of females to skip reproduction in some years appear to foster the high repeatability of reproductive traits. Our research and previous studies indicate that many, but not all, reproductive traits in female snakes are highly repeatable. The repeatability of a few traits, particularly post-partum female condition, is likely to depend strongly on the reproductive mode of the species.

Use of a programmed temperature vaporizer and an in situ derivatization reaction to improve sensitivity in headspace-gas chromatography. Application to the analysis of chlorophenols in water

In the present work we propose the combined use of a derivatization reaction within the vial of a headspace sampler with a programmed temperature vaporizer (PTV) inlet in the solvent vent mode as a new methodology for obtaining an increase in sensitivity in headspace-gas chromatography (HS-GC) for the analysis of sparingly volatile compounds. As test analytes the following chlorophenols were used: 2-chlorophenol (2CP), 2,4-dichlorophenol (24DCP), 4-chloro-3-methylphenol (4C3MP) and 2,4,6-trichlorophenol (246TCP). The derivatization reaction was carried out with acetic anhydride because it can be carried out in situ in aqueous medium. In the programmed temperature vaporizer inlet, three different liners, one of them empty and the others with materials of different trapping strengths (glass wool and Tenax-TA), were compared. The best results were obtained when an empty liner was used, with better repeatability and S/N ratios. In the case of the liner filled with Tenax-TA, a considerable lack of repeatability was observed, this being attributed to interactions between the derivatized compounds and the adsorbent. The proposed methodology affords very low limits of detection, in the range of a few ng/L for all the compounds, with good precision and accuracy values.

Reliability and diagnostic significance of frequency doubling visual field testing

Abstract Purpose The aims of this study were to compare results of Frequency Doubling Perimetry (FDP) with the gold standard of Humphrey Visual Field Testing (HVF). To determine the reliability and repeatability of FDP, and whether referrals had diagnostic significance. Methods Notes collected of patients referred from the community because of abnormal visual fields, tested by FDP. Information gathered on proforma included reason for referral, place of referral, number of defects in both eyes, whether they were repeatable, consistent with HVF, reliability, follow‐up and diagnosis. Results 49 case notes were collected and reviewed, 98 eyes included. 31 females (63%), 18 males (37%). Mean age 59.5. All patients were referred because of VF defect. In 21 patients (43%), this was the only reason for referral. FDP showed poor consistency with HVF. This may be because it detects field loss earlier in the disease process. However, there was a lack of repeatability in FDP testing. In 29% of referrals, tests were not repeated, even though each test takes less than 90 seconds. FDP showed high reliability, possibly because it is a shorter test, simpler to perform and requiring less concentration Most patients were discharged at first or second appointment. Patients were seen an average of 2.6 times. The number diagnosed with glaucoma are very low (3), and the number labelled ‘glaucoma suspects’ higher (6). These patients are unlikely to have been detected without this technology. Conclusion In our study, FDP showed poor correlation with HVF. The lack of repeatability between field defects in FDP casts doubts on its validity of screening for glaucoma.Most patients were not diagnosed with glaucoma, ocular hypertension or glaucoma suspects following assessment.

Crack Detection in an Embedded Spindle using Broadband Modal Excitation

This paper demonstrates a methodology for detecting cracks in a metal spindle, which is housed within a military vehicle wheel end assembly. A finite element model is used to estimate the undamped natural frequencies of the raw spindle. Additional mass and stiffness is then added to a simplified model of the spindle to simulate sources of variability within the assembly. Spindles are tested outside the wheel end assembly to compare the responses of undamaged and cracked spindles. A hypothesis testing approach is developed to detect the presence of a crack based on damage indices involving the summation and multiplication of spectral energies. Experiments on wheel assemblies mounted on a vehicle with the vehicle lifted off the ground are performed to demonstrate that the wheel assemblies can be nondestructively evaluated to identify cracks of varying depths despite sources of variability due to the presence of the brake drum, lack of repeatability in the sensor attachment, and other issues.

Micro-extrusion of ultrafine grained copper

Because of the well known virtues of low cost and high productivity, metal forming technology is well suited for mass production of metal micro-components. However, scaling down metal forming processes proves to be problematic because, among other factors, the relatively coarse grain (CG) structure of micro-billets leads to non-uniform material flow and lack of repeatability during microforming. A substantial grain size reduction below one micron should help to prevent these problems. The aim of the presented study is to investigate a possibility of using an ultrafine grained (UFG) metal for micro-extrusion. The material used for this purpose is CP Cu often used for electrical applications. The UFG version of Cu is produced by severe plastic deformation at room temperature using up to 8 passes of equal channel angular pressing. The microstructure and compression properties of the UFG version of the material are tested. The microforming process of backward extrusion is carried out at room temperature using half cylindrical billets. The extrusion force, grain flow, shape representation and surface quality of the extruded micro-components are compared.

Susceptibility to Heterobasidion parviporum in Picea abies clones grown in different environments

SummaryThirty‐five Norway spruce, Picea abies, clones from Sweden were tested for resistance to Heterobasidion parviporum. Rooted cuttings of the clones were planted in Italy and Greece and cultivated for two growing seasons before inoculation with H. parviporum. Extent of infection was determined 6 weeks later. The results were compared to those of earlier inoculations in Sweden. Plant growth traits were under strong genetic control in all locations with broad sense heritability estimates between 0.14 and 0.54. Lesion and fungal extension heritabilities were moderate, H2 ranged from 0.09 to 0.20, and exhibited rather large genetic variation. There was significant genotypic correlation between Italy and Greece with respect to both lesions and fungal extension. No such correlations were found between Sweden and the two other countries. The lack of repeatability in testing susceptibility is unsatisfactory. It could be explained by C‐effects associated with propagation of the host plants. Height growth correlated significantly and positively among all countries.

Liquid chromatography at the critical conditions in pure eluent: An efficient tool for the characterization of functional polystyrenes

Functional polymers are usually separated by liquid chromatography at critical conditions (LC-CC) using a desorli/adsorli mixture as eluent. In this paper, we describe LC-CC using dimethylformamide (DMF) as pure eluent at 72 °C and its application to the analysis of functional polystyrenes. The critical adsorption point is reached by tuning the temperature so that the lack of repeatability is no longer a problem. We analysed several batches of polystyrenes, exhibiting different molecular weights and functionalities. We were able to differentiate di-, mono- and non-functional polystyrenes, bearing carboxylic acid, hydroxyl or nitroxide moieties. The behaviour of these polystyrenes expressed by the experimental results was compared with their behaviour described by the LC-CC theory through the calculation of the effective interaction parameter of each end group. The technique also makes it possible to quantify the fractions of different functional polymers in a blend.

Design of a conductivity meter for highly insulating liquids

The accurate measurement of the electrical conductivity of low conducting liquids is an important issue in many industrial applications. The lack of repeatability is a common problem to the available procedures and commercial techniques. In this paper, we present a device to measure the electrical conductivity of low conducting liquids. The variable inter-electrode gap allows us to assure the existence of an ohmic regime, since only under ohmic regime conditions is the value of the conductivity meaningful.

Relative Resistance Chemical Sensors Built on Microhotplate Platforms

AbstractThe selectivity, sensitivity, and speed of metal oxide conductometric chemical sensors can be improved by integrating them onto micromachined, thermally-controlled platforms (i.e., microhotplates). The improvements largely arise from the richness of signal inherent in arrays of multiple sensing materials and the ability to rapidly pulse and collect data at multiple temperatures. Unfortunately, like their macroscopic counterparts, these sensors can suffer from a lack of repeatability from sample-to-sample and even run-to-run. Here we report on a method to reduce signal drift and increase repeatability that is easily integrated with microhotplate chemical sensors. The method involves passivating one of a pair of identically-formed sensors by coating it with a highly electrically resistive and chemically impermeable film. Relative resistance measurements between the active and passive members of a pair then provide a signal that is reasonably constant over time despite electrical, thermal and gas flow rate fluctuations. Common modes of signal drift, such as microstructural changes within the sensing film, are also removed. The method is demonstrated using SnO2 and TiO2 microhotplate gas sensors, with a thin Al2O3 film forming the passivation layer. It is shown that methanol and acetone at concentrations of 1 µmol/mol, and possibly lower, are sensed with high reproducibility.

Validation of a New Endoscopic Technique to Assess Acid Output in Zollinger–Ellison Syndrome

To safely manage the hypersecretory state in patients with Zollinger-Ellison syndrome, both upper endoscopy and gastric analysis are required to titrate optimal medical therapy. Conventional gastric analysis requires more than 1 hour to perform and results in significant patient dissatisfaction. In this study, we have validated endoscopic gastric analysis as a novel technique that can effectively replace conventional gastric analysis. In a prospective, cross-over study, 12 patients with Zollinger-Ellison syndrome underwent gastric analysis, first by the conventional method and then by an endoscopic technique performed on the same day. Acid concentration was determined by titration, volume output was recorded, and acid output was calculated using standard methodologies and formulas. Agreement was assessed following the Bland-Altman method. To assess repeatability, both techniques were repeated on the same day in a subset of patients. Excellent agreement was reported between acid output (95% limits of agreement, -1.27 to 1.61 mEq/h) and acid concentration (95% limits of agreement, -0.01 to 0.01 mEq/mL), although poor agreement was observed between volume output measured. Endoscopic gastric analysis showed greater reproducibility regarding acid and volume output measured. We introduce a new, rapid, reproducible, and accurate endoscopic technique to measure acid output in patients with Zollinger-Ellison syndrome who require both annual endoscopy and gastric analysis. The data presented here suggest that endoscopic gastric analysis would be equally effective in determining acid output in other hypersecretory states. Additional analysis of cost effectiveness is needed to evaluate its use as a screening tool in select populations.