Positive display polarity is particularly advantageous for small character sizes: implications for display design.

Summary form only given. We present here the results of a series of experiments comparing the operation of an X-pinch in positive and negative polarity. Of particular interest are the X-ray yield, timing, radiating spot size, and the number of radiating spots in a given X-pinch. Conventionally, an X-pinch is operated in negative polarity resulting in electric field lines that terminate on the wires. This choice of polarity for the generator is due to the fact that breakdown in these machines is easier to prevent when they are operated in negative polarity. Previous experiments involving single wire explosions at low current (1-5 kA) have shown that more energy can be deposited in the wire cores when they are driven in positive as opposed to negative polarity. These results raised the question of what happens when pinch-type experiments are driven in positive polarity. Recently, it has become possible to use the 450 kA XP pulser at Cornell to drive X-pinches in positive polarity. The positive polarity condition is established by inserting a convolute before the load and this results in electric field lines that originate on the wires of the X-pinch. This arrangement added complexity and inductance to the positive polarity shots, making it difficult to directly compare results from positive and negative shots. More recently, the entire pulser was switched to positive polarity. This allows a more direct comparison between positive and negative polarity X-pinch operation

It is commonly assumed that comparative coherence relations (e.g., Peter is tall but his brother is short) can be analyzed in terms of semantic contrast. In this article it is claimed that comparative relations need to be understood in a context containing a similarity assumption. This assumption may be con®rmed (positive polarity) or denied (negative polarity) by the comparative text passage. When two entities are characterized in terms of a common variable without a similarity assumption being present (e. g., Peter's favorite color is red. His brother prefers green), the coherence relation is merely additive. Additive relations are not de®ned for polarity. While comparative relations may be linguistically marked by connectives like but, by contrast, or and in English or maar, daarentegen, or en in Dutch, additive relations remain unmarked. The distinction between comparative and additive relations is empirically supported by a corpus-based study of the linguistic marking of similarities and di€erences between the price movements of shares, using 400 fragments from stock-market reports in a Dutch daily newspaper. Some of these fragments clearly invoke similarity assumptions, for instance because of the fact that two companies are in the same branch of industry or because the fragment is preceded by an announcement of the general trend in share prices on a particular day. It was found that the overwhelming majority of linguistic markers of similarities and di€erences in share price movements occurred in contexts containing similarity assumptions. For instance, similarities that were to be expected may be marked by en `and' (e.g., Elsevier gained 1.10 [en] Kluwer went up forty cents), while unexpected di€erences are often marked by daarentegen `by contrast' (e.g., Elsevier gained 1.10 (new price 67.80). [Daarentegen] Kluwer lost forty cents (new price 50.70)). Some apparent counterexamples, in which two companies from the same branch of industry show di€erent share price movements while this di€erence remains unmarked, in fact do not invalidate the similarity assumption framework but Cognitive Linguistics 10±2 (1999), 147±184 0936±5907/99/0010±0147 # Walter de Gruyter support it. In the majority of these cases the similarity assumption has been eliminated or weakened by earlier announcements of di€erences within a certain branch. A closer analysis of ®ve Dutch comparative connectives reveals that two dimensions of comparative polarity need to be distinguished: a propositional polarity parameter with the values ``di€erence'' and ``similarity'', and an assumptional polarity parameter distinguishing between con®rmations and denials of the relevant assumption. Di€erent linguistic elements may be characterized in terms of di€erent polarity dimensions. For instance, ook `also' expresses positive propositional polarity, while maar `but' is an indication of negative assumptional polarity.

The effect of aquarium color background on the survival, growth performance, body coloration, and enzymatic activity of laboratory cultured Cherax quadricarinatus juveniles

One of the main advantages of the MIG/MAG process is its high productivity. In most of the applications, positive polarity is used, due to its greater arc stability, generation of less splatter and formation of weld beads with suitable geometry. However, in some applications, there is a need for greater production capacity than that offered by conventional MIG/MAG welding. In the literature, it is stated that negative polarity provides a higher fusion rate than positive, despite leading to a high level of splatter and unsuitable formation of the weld bead. Unfortunately, there is not much information available on the effects of the process variables in this polarity, much less justification for such. Therefore, this work is an attempt to try to understand the reason why there is a higher deposit rate in negative polarity, as well as the related effect on the geometry of the weld beads. To do this, comparative MIG/MAG welds were produced in both positive and negative polarities, using two compositions of shielding gases at two current values. The transfer mode and the behaviour of the arc were analysed by synchronized profiling. The geometric profile of the weld bead was evaluated by means of metallographic procedures. From the results, which disagree in part with the current literature, it was seen that both the transfer mode as well as the morphology and the appearance of the weld bead are dependent on the composition of the shielding gas. To explain the phenomena inherent in the greater fusion rate of wire in DC − , the suggestion is that the fact that arc scales the sides of the wire in this polarity may be the governing factor.

Matrix effect is the effect on an analytical method caused by all other components of the sample except the specific compound to be quantified. Matrix effects and selectivity issues have long been associated with bioanalytical techniques. A number of approaches have been investigated to improve reproducibility and robustness of LC-MS-MS methods that are subjected to matrix effects. In the present research work the role of ionization polarity on matrix effect was studied. Enalapril and its metabolite were analyzed in positive and negative polarity by using ESI-LC-MS/MS. Matrix factor (MF) was determined to evaluate the matrix effects in different polarities. Two different concentration levels of each analyte were used to determine the MF. In positive polarity the MF at two different concentration levels were 0.6353 & 0.6496 for enalapril and 0.6885 & 0.6770 for enalaprilat, whereas, the MF in negative polarity at two different concentration levels were 0.8203 & 0.7717 for enalapril and 1.1124 & 1.0915 for enalaprilat. These data showed approximately 30-35% ion suppression in positive polarity for both the analyte, but approximately 20% ion suppression for enalapril and 10% ion enhancement for enalaprilat in negative polarity. So, matrix effects depend on the ionization polarity also.

The increasing use of online resources in emergency medicine (EM) education has driven demand for higher quality resources. Learning experience design (LED) is the study of how electronic user interfaces impact learner outcomes. We sought to summarize the evidence for LED principles to inform creation of EM educational resources. We performed scripted searches of MeSH terms, PubMed keywords, and hand tracings. Inclusion criteria were controlled studies using light-emitting diode or liquid crystal display monitors with Latin-based languages. Cathode ray tube (CRT) monitors were excluded because of the user experience confounders. Thirty-two articles met inclusion criteria. Overall, 14-point size significantly improved legibility compared to smaller font sizes. Similarly, Verdana and Arial typefaces significantly improved legibility compared to Times New Roman typeface. Verdana also significantly decreased subjective mental workload and visibility difficulty ratings and required the least eye movement of any typefaces tested. Positive polarity (dark text on light background) significantly improved reading outcomes across many measurements over negative polarity. There was higher character identification accuracy with higher luminance. Text effects (e.g., italics), interword and interletter spacing, and page presentation are among variables with mixed or minimal evidence. Learning experience design principles significantly impacted reading and learning outcomes in laboratory settings. No studies evaluated classroom outcomes. Recommendations for electronic learning environments are 14-point font with Verdana or Arial typeface with positive polarity (dark letters on light background). We recommend increasing screen brightness slightly. EM educators may significantly improve the speed and accuracy of learning written material by espousing evidence-based LED principles.

This paper presents the research results on the effect of internal impurity of palm oil and needle electrode polarity on the breakdown voltage. The electrodes used in this research were in an arrangement of needle-plate with the needle sharpness angles used were 45° and 60°. A DC high voltage has been used as the testing voltage during experiment with the spark gap between the needle and plate electrodes was 2.5mm and 5mm. Breakdown testing has been done using two polarities on the needle electrodes, which were positive and negative polarities. Before the exposure to electric field, microscopically an unused palm oil looked clear and did not reveal any impurity. The solid impurities started to appear in the oil once it was exposed to electric field. It was originated from the fat contained in the palm oil. Under the influence of electric field, the impurities were moving and gathering around the tip of the needle electrode, the part with the highest field intensity. The largest amount of internal impurities around the needle tip has been found during the experiment with the needle sharpness angle of 60°, meaning that sharper the needle point, larger would be the amount of impurities gathered around. Considering the two spark-gap distances and the two needle sharpness angles used in the research, it was found that the level of breakdown voltage at positive polarity is smaller than the breakdown voltage level at negative polarity.

In the present paper some numerical results, based on the theory developed in double and third scattering approximation are presented. The influences of microphysical and morphological properties of discrete random medium on photometric and polarimetric characteristics of backscattered radiation are discussed. If the effective refractive index of the medium is kept the same, the differences in the features of the opposition effects are caused by differences in the microscopic characteristics of the scatterers. From theoretical observations, it is concluded that the results demonstrate that the state of polarization of the back scattered radiation is controlled by the state of polarization of singly scattered radiation. It is well known that the positive polarization of light scattered by isolated particle leads to a negative polarization feature in the backscattering direction. The angular dependence of the polarization state for wavelength sized spherical particles is much more complex and oscillatory. The interference may lead to a more complex dependence of polarization on the scattering angle, with positive and negative polarization regions appearing simultaneously. The resulting interference of doubly scattered waves can result in positive polarization as well as negative polarization.

There are many sets of guidelines concerning the accessibility of the web for older adults, but little empirical evidence from studies with older people to support their recommendations. In addition, all the recommendations apply to text in languages using the Latin alphabet. This study investigated the effects of text color and background color on the performance and preferences of younger and older adults on webpages in the Thai language. There were 18 Thai younger participants (19 - 29 years) and 18 Thai older participants (59 - 70 years). There were three combinations of text color and color (black text on white background, white text on black background, and sepia text on off-white background). The text and background color combinations failed to have any significant effects on the performance measures of task completion rate or time spent skim reading webpages. However, for the preference measure, there was a significant difference between combinations of text and background color but no differences between the age groups. There was also a significant interaction between combinations of text and background color and age group. These results form an useful basis for web design guidelines for Thai websites for text and background color for both younger and older users.

This study aimed to explore how different presentation modes of graphical icons affect the viewer’s attention. The relevant experiment was designed to investigate three main variables: icon composition, polarity, and border. Through permutation and combination, six presentation modes were obtained as follows: line + positive polarity + border (M1), plane + positive polarity + border (M2), line + negative polarity + border (M3), plane + negative polarity + border (M4), line + positive polarity + no border (M5), and plane + positive polarity + no border (M6). Thirty-six participants were required to watch thirty stimuli, or graphical icons, presented concurrently in six abovementioned modes. The number of first fixations was recorded by eye-trackers; meanwhile, subjective evaluation of attention was conducted and analyzed. As indicated by the experimental results, the icons presented in M4 attracted the most attention; in contrast, the icons presented in M5 attracted the least attention. The findings herein can be used as a reference by interface designers while icons are being designed.KeywordsEye-trackingLine compositionPlane compositionPositive polarityNegative polarityWith borderBorderless

The object of research is a circuit that simulates a lightning strike to a tower of 220 kV power transmission line, taking into consideration the reflection of a current wave from 10 nearest towers. Computation of the voltage arising at the top of the struck tower is necessary further to determine the lightning performance of transmission line by various methods. The lightning current has several maxima, in the case of a positive impulse polarity and, accordingly, several minima, in the case of a negative polarity, which are generally being called peaks. In addition, the lightning current impulse has a non-constant steepness in the entire area of current rise up to the first peak. The approximation of the real lightning current by simplified mathematical expressions cannot take into account all its real features. For a more detailed study of transient processes caused by thunderstorm activity, there is a need to use oscillograms of real lightning currents when modeling. The problem of determining the voltage at the top of the stricken transmission line tower was solved using circuit simulation. For an in-depth study of how the shape of the lightning current impulse affects the shape of the voltage at the top of the tower struck, digitized oscillograms of real lightning currents were used. The simulation was carried out for 7 negative lightning impulses with the first peak varying from –33.380 kA to –74.188 kA. In the case of positive lightning, 3 oscillograms were used with the first peak varying from +38.461 kA to +41.012 kA. The article shows that the shape of the front of the lightning current impulse and the amplitude of the first peak of the lightning current have a decisive effect on the maximum voltage value at the top of a power transmission line tower struck by lightning. The maximum voltage occurs precisely at the front of the current wave before the first peak of the lightning current. Therefore, the back flashover of the insulation from the tower to the phase conductor is most likely at a moment in time at the front of the current wave. By the time the maximum current is reached, the voltage at the top of the tower will be reduced by several tens of percent, compared to the maximum voltage at the tower, which occurs much earlier at the front of the current wave. The conducted research contributes to the development of methods for calculating the lightning performance of power lines and extends the scope of application of circuit simulation programs.

Sulphur hexafluoride (SF6) is the most commonly used dielectric gas in electrical systems, DC-GIL is considered as a new type of transmission lines has the potential to replace the overhead lines and cables in the future for use in DC distribution networks. It deserves great concern that abundant amount of SF6 use in the earth's atmosphere because this gas is known to be a kind of "greenhouse gas". Also, metal particles inevitably appearing in the pipeline of DC GIL which may do damage to GIL and cause a serious threat to its insulation safe and reliable operation. This paper aims to focus on experimental study on the difference in insulation strength of SF6 gas and the mixture of two gases (SF6 and N2) with and without using conducting particle under DC voltage in the ball-bowl electrode arrangement. Moreover, spherical conducting particle is selected to simulate metal particle defects in GIL and they are set to the floating position. Breakdown characteristics of SF6 gas and (SF6-N2) gas mixtures have been measured in non-uniform electric field when the SF6 gas mixture ratio (70%, 50%, 30% and 20%) and the pressure is between 0.1MPa and 0.5MPa under the positive and negative polarity of DC voltage. The experiment results show that DC negative polarity is more severe as compared with positive polarity. In addition, it is found that there is no significant increase in breakdown voltage when the pressure is more than 0.3MPa in the presence of particle but the growth trend is clear without particle. The equivalencies between the breakdown voltage of SF6 and SF6-N2 gas mixtures were analyzed with and without the presence of conducting spherical particle and tried to predict the improved breakdown voltage SF6-N2 gases mixture using Artificial Neural Network technique.

Streamer initiation has been studied in cyclohexane, Midel 7131 (ester based dielectric liquid) and Nytro 10X (mineral transformer oil). Experiments were conducted in point-plane geometry under 40 ns/740 /spl mu/s impulse voltage. The tip electrode was electrochemically etched to approximately 2.0 /spl mu/m, the electrode gap was approximately 18 mm. A sensitive differential charge measurement technique was used to measure the injected charge. Shadow graphics was used to acquire images of streamers, and a photomultiplier was utilized to study light emission under positive polarity in Nytro 10X. The experimental setup is capable of measuring injected charges down to 0.1 pC, the shadow graphics has an image resolution of 1 /spl mu/m and the photomultiplier can detect light down to the order of single photons. For all three liquids a small pre-inception current at voltages below streamer inception was found with positive point polarity; no emitted light from this current in Nytro 10X was detected. No preinception current was observed under negative polarity in any of the liquids.

Ionic liquid ion sources: characterization of externally wetted emitters

Advanced characterization of the products of the hydrotreatment of gas oils is of high interest for refiners and can be achieved using ultrahigh resolution mass spectrometry (FT-ICR MS). However, the analysis of gas oil samples by FT-ICR MS generates complex data sets with numerous variables whose exhaustive analysis requires the use of multivariate methods. Relevant information about nitrogen and sulfur compounds contained in several industrial gas oils are obtained by using three different ionization modes that are electrospray ionization (ESI) used in positive and negative polarities and atmospheric pressure photoionization (APPI) used in positive polarity. For data sets generated for a single ionization mode, classical multivariate methods such as Principal Component Analysis (PCA) are commonly used. When the key information is spread into several ionization modes and thus into several data sets, a data fusion approach is highly interesting to simultaneously explore these data sets and can be followed by Parallel Factor analysis (PARAFAC). Nevertheless, many more variables are simultaneously considered when data fusion is performed and the sensitivity of PARAFAC and its ability to extract the most relevant variables compared to classical multivariate methods has not been assessed yet in the framework of FT-ICR MS. In this paper, a comparison of the classical data analysis (PCA) approach and the data fusion combined with the PARAFAC analysis approach is presented. The results have shown that applying PARAFAC on fused data sets is highly sensitive and able to put forward features and variables that are individually identified through classical data analysis with greater ease of implementation and interpretation of results. As an example, dibenzothiophenes and carbazole families (DBE 9) have explained most of the variance between samples and remain the most refractory compounds in hydrotreated samples. A significant difference in alkylation between the different types of gas oils has also been spotted. This paper validates the power and efficiency of this approach to explore complex data sets simultaneously without any loss of significant information.