Red Phase Research Articles

A correlation between GALEX FUV magnitude and chromospheric activity among red giant stars

AbstractIt is shown that upon combining GALEX far-ultraviolet and Johnson B magnitudes a resultant FUV–B colour can be obtained that for red giant stars of luminosity classes III and II correlates well with chromospheric emission in the cores of the Mg iih and k lines. Giant stars throughout the colour range 0.8 ≤ B – V ≤ 1.6 exhibit such a phenomenon. The main result of this paper is to show that GALEX far-ultraviolet photometry can provide information about the degree of chromospheric activity among red giant stars, and as such may offer a tool for surveying the evolution of chromospheric activity from the main sequence into the red giant phases of stellar evolution.

Fires Following Bark Beetles: Factors Controlling Severity and Disturbance Interactions in Ponderosa Pine

Previous studies have suggested that bark beetles and fires can be interacting disturbances, whereby bark beetle-caused tree mortality can alter the risk and severity of subsequent wildland fires. However, there remains considerable uncertainty around the type and magnitude of the interaction between fires following bark beetle attacks, especially in drier forest types such as those dominated by ponderosa pine (Pinus ponderosa Lawson & C. Lawson). We used a full factorial design across a range of factors thought to control bark beetle-fire interactions, including the temporal phase of the outbreak, level of mortality, and wind speed. We used a three-dimensional physics-based model, HIGRAD/FIRETEC, to simulate fire behavior in fuel beds representative of 60 field plots across five national forests in northern Arizona, USA. The plots were dominated by ponderosa pine, and encompassed a gradient of bark beetle-caused mortality due to a mixture of both Ips and Dendroctonus species. Non-host species included two sprouting species, Gambel oak (Quercus gambelii Nutt.) and alligator juniper (Juniperus deppeana Steud.), as well as other junipers and pinyon pine (Pinus edulis Engelm.). The simulations explicitly accounted for the modifications of fuel mass and moisture distribution caused by bark beetle-caused mortality. We first analyzed the influence of the outbreak phase, level of mortality, and wind speed on the severity of a subsequent fire, expressed as a function of live and dead canopy fuel consumption. We then computed a metric based on canopy fuel loss to characterize whether bark beetles and fire are linked disturbances and, if they are, if the linkage is antagonistic (net bark beetle and fire severity being less than if the two disturbances occurred independently) or synergistic (greater combined effects than independent disturbances). Both the severity of a subsequent fire and whether bark beetles and fire are linked disturbances depended on the outbreak phase of the bark beetle mortality and attack severity, as well as the fire weather (here, wind). Greater fire severity and synergistic interactions were generally associated with the “red phase” (when dead needles remain on trees). In contrast, during the “gray phase” (when dead needles had fallen to the ground), fire severity was either similar to, or less than, green-phase fires and interactions were generally antagonistic, but included both synergistic and neutral interactions. The simulations also revealed that the magnitude of the linkage between these two disturbances was smaller for fires occurring during high wind conditions, especially in the red phase. This complexity might be a reason for the contrasted or controversial perception of bark beetle-fire interactions reported in the literature, since both fire severity and the type and magnitude of the linkage can vary strongly among studies. These results suggest that, for fires burning in the gray phase following moderate levels of mortality, bark beetle-caused mortality may buffer rather than exacerbate fire severity. However, for fires burning under high wind speeds, regardless of the outbreak phase or level of mortality, the near complete loss of canopy fuels may push this ecosystem into an alternative state dominated by sprouting species.

Fabrication and characterization of polydiacetylene supramolecules in electrospun polyvinylidene fluoride nanofibers with dual colorimetric and piezoelectric responses

The ability to prepare Polydiacetylenes based materials in the polyvinylidene fluoride matrix polymer is interesting due to the combination of colorimetric and electrical signaling. The new PVDF/PDA composite nanofibers were prepared via the electrospinning method. The self-assembly of diacetylene monomers (PCDAs) occurred during the electrospinning process. The assembled diacetylene monomers in the PVDF nanofibres were further polymerized to form PDA. Full factorial experimental design was applied to investigate the influence of PVDF concentration and PCDA content on the morphology of nanofibers. The colorimetric transitional of the uniform and beadless PVDF/PDA nanofibers were studied as a function of temperature. The crystal polymorphism of these structures were evaluated using Fourier transform infrared, differential scanning calorimetry, and wide angle X-Ray diffraction. The piezoelectric response of the PVDF/PDA nanofibers in the red and blue phases was also measured. The results showed that a combination of colorimetric and piezoelectric responses is available with composite nanofibers of PVDF/PDA. The polymorphism investigation demonstrated that assembled PCDAs have the effect of inhibiting the growth of non-polar α phase crystals, while promoting the growth of polar β phase. Moreover, the electrospun PVDF/PCDA nanofibers after UV-irradiation and formation of PDA exhibited greater intensity of β-phase in comparison to that before irradiation. However, the red phase of PVDF/PDA nanofibers indicated less fraction of β-phase than the blue phase. The blue-to-red color transition of PVDF/PDA composite nanofibers accompanied by the variation of piezoelectric response could open new avenues for many sensor applications.

Predicting the locations of possible long-lived low-mass first stars: importance of satellite dwarf galaxies

The search for metal-free stars has so far been unsuccessful, proving that if there are surviving stars from the first generation, they are rare, they have been polluted, or we have been looking in the wrong place. To predict the likely location of Population~III (Pop~III) survivors, we semi-analytically model early star formation in progenitors of Milky Way-like galaxies and their environments. We base our model on merger trees from the high-resolution dark matter only simulation suite \textit{Caterpillar}. Radiative and chemical feedback are taken into account self-consistently, based on the spatial distribution of the haloes. Our results are consistent with the non-detection of Pop III survivors in the Milky Way today. We find that possible surviving Population III stars are more common in Milky Way satellites than in the main Galaxy. In particular, low mass Milky Way satellites contain a much larger fraction of Pop~III stars than the Milky Way. Such nearby, low mass Milky Way satellites are promising targets for future attempts to find Pop~III survivors, especially for high-resolution, high signal-to-noise spectroscopic observations. We provide the probabilities for finding a Pop~III survivor in the red giant branch phase for all known Milky Way satellites to guide future observations.

Morphology-Dependent Cell Imaging by Using a Self-Assembled Diacetylene Peptide Amphiphile.

Herein, a novel cationic peptide gemini amphiphile containing diacetylene motifs (DA2 P) is presented, which self-assembles into novel tadpole- and bola-shaped nanostructures at low concentrations and nanofibers at higher concentrations. Interestingly, the DA2 P assemblies can be polymerized into a fluorescent red phase but only during incubation with HeLa cells, most likely owing to the reorganization of the diacetylene chains of DA2 P upon interaction with the cell membrane. The red-fluorescent polymerized DA2 P assemblies can serve as a novel cell imaging probe. However, only vesicles, tadpole- and bola-shaped DA2 P assemblies can be translocated into HeLa cells, whereas the nanofiber-like DA2 P assemblies are trapped by the cell membranes and do not enter the cells. Hence, morphology-dependent cell imaging is observed.

Morphology‐Dependent Cell Imaging by Using a Self‐Assembled Diacetylene Peptide Amphiphile

AbstractHerein, a novel cationic peptide gemini amphiphile containing diacetylene motifs (DA2P) is presented, which self‐assembles into novel tadpole‐ and bola‐shaped nanostructures at low concentrations and nanofibers at higher concentrations. Interestingly, the DA2P assemblies can be polymerized into a fluorescent red phase but only during incubation with HeLa cells, most likely owing to the reorganization of the diacetylene chains of DA2P upon interaction with the cell membrane. The red‐fluorescent polymerized DA2P assemblies can serve as a novel cell imaging probe. However, only vesicles, tadpole‐ and bola‐shaped DA2P assemblies can be translocated into HeLa cells, whereas the nanofiber‐like DA2P assemblies are trapped by the cell membranes and do not enter the cells. Hence, morphology‐dependent cell imaging is observed.

The direct identification of core-collapse supernova progenitors.

To place core-collapse supernovae (SNe) in context with the evolution of massive stars, it is necessary to determine their stellar origins. I describe the direct identification of SN progenitors in existing pre-explosion images, particularly those obtained through serendipitous imaging of nearby galaxies by the Hubble Space Telescope I comment on specific cases representing the various core-collapse SN types. Establishing the astrometric coincidence of a SN with its putative progenitor is relatively straightforward. One merely needs a comparably high-resolution image of the SN itself and its stellar environment to perform this matching. The interpretation of these results, though, is far more complicated and fraught with larger uncertainties, including assumptions of the distance to and the extinction of the SN, as well as the metallicity of the SN environment. Furthermore, existing theoretical stellar evolutionary tracks exhibit significant variations one from the next. Nonetheless, it appears fairly certain that Type II-P (plateau) SNe arise from massive stars in the red supergiant phase. Many of the known cases are associated with subluminous Type II-P events. The progenitors of Type II-L (linear) SNe are less established. Among the stripped-envelope SNe, there are now a number of examples of cool, but not red, supergiants (presumably in binaries) as Type IIb progenitors. We appear now finally to have an identified progenitor of a Type Ib SN, but no known example yet for a Type Ic. The connection has been made between some Type IIn SNe and progenitor stars in a luminous blue variable phase, but that link is still thin, based on direct identifications. Finally, I also describe the need to revisit the SN site, long after the SN has faded, to confirm the progenitor identification through the star's disappearance and potentially to detect a putative binary companion that may have survived the explosion.This article is part of the themed issue 'Bridging the gap: from massive stars to supernovae'.

A semi-analytic approach to model signal plans in urban corridors and its application in metaheuristic optimization

ABSTRACTThis article introduces a new formulation for modeling and evaluating the effects of traffic signal timing over arterial roads, based on the Lighthill Whitham Richards model. We introduce a Hamilton–Jacobi formulation of the traffic model, in which the red phases of the traffic signals are described as internal conditions corresponding to a zero flow (fixed bottlenecks). With this approach, it is possible to model and evaluate the traffic signal timings accurately and efficiently. We then integrate this fast simulation scheme into an optimization framework for computing the optimal signal timing strategy associated with a given set of initial and boundary conditions, over a transportation network. A numerical implementation is shown for a single link case and for a more complex signalized intersection.

Self-assembly and photopolymerization of a novel quaternary-ammonium functionalized diacetylene on noble metal nanoparticles: A comparative study

Abstract Stable hydrosols of gold and silver nanoparticles coated with the quaternary-ammonium group endowed diacetylene DAAMM (N,N,N-trimethyl-3-(pentacosa-10,12-diynamido)propan-1-ammonium) were obtained through a ligand-exchange reaction leaving the morphology of the pristine cores unmodified. Photopolymerization of the chemisorbed diacetylene shell occurred in both red and blue phases thanks to the presence of internal, H-bondable amide functions in the monomer chain, which are supposed to help the formation of a packed bilayer on the metal surfaces. Multidisciplinary characterization of the polymerized samples, including spectroscopic, morphological and thermal techniques, highlighted that differences occur in the polymerization process on gold and silver nanoparticles under different experimental conditions, suggesting a higher affinity of the trimethylammonium headgroup for gold substrates in acidic media. With respect to the extensively investigated PCDA (pentacosa-10,12-diynoic acid), DAAMM showed reduced capability of photogenerating thick polymer shells, especially in the more delocalized blue form, probably because of the inefficiency of the cationic monomer to form the multi-bilayered architecture typical of the highly-performing, carboxyl-terminated diacetylene. On the other end, the inner cross-linked structure gives to poly(DAAMM)-coated nanohybrids increased stability in water with respect to self-assembled counterparts deriving from saturated cationic surfactants, making them a promising sensing platform for rapid and cost effective assays of real samples.

Transfer of molecular chirality to spiral nanostructure in the interfacial mixed amphiphilic diacetylene/histidine monolayers via in situ topochemical photopolymerization

The photopolymerization in the monolayers consisted of an equivalent mixture of 10, 12-pentacosadiynoic acid and amphiphilic histidine derivatives L-HC18 or D-HC18 has been investigated. It is found that the diacetylene derivatives can be incorporated into the monolayer and polymerized to polydiacetylene (PDA) backbone with a red phase by in situ UV irradiation at the air/water interface. The chiral amphiphiles L-HC18 or D-HC18 can transfer the molecular chirality to PDA through the ordered alignments of the two components. AFM images of the transferred films further revealed the chiral nanostructures from PDA/L-HC18 or PDA/D-HC18. The topochemical polymerization of the mixed films at a low surface pressure as a function of time is carried out to characterize crimp behaviors from straight nanobelts to more curly bands even spiral nanostructures in a clockwise or anti-clockwise direction, in which the curling direction is depended on the molecular chirality of the two enantiomers. The research has well established the connection between molecular chirality and mesoscopic chirality using the Langmuir as well as Langmuir-Blodgett methods.

Insight into diacetylene photopolymerization in Langmuir‐Blodgett films using simultaneous AFM and fluorescence microscopy imaging

A phase‐separated monolayer film comprised of a mixture of 10, 12‐pentacosadiynoic acid (PCDA) with perfluorotetradecanoic acid (PF; CF3(CF2)12COOH) has been characterized using a microscope that is capable of simultaneous atomic force microscope (AFM) imaging and fluorescence imaging. Design criteria for this instrument are described, as well as its application to investigating the mixed film systems. The product of PCDA photopolymerization has two phases, a red phase with strong fluorescence and a blue phase with no fluorescence. With the help of the dual AFM‐fluorescence microscope, it was found that both the red and the blue phase polymers were produced in the same sample from photoillumination, and the relative quantities of the different phases were quantified. Further, the importance of intrinsic mechanical stress in the films is discussed in terms of its influence on selectivity towards the red polymer phase.

Color Phase—Specific Ion Regulation of the European Green CrabCarcinus maenasin an Oscillating Salinity Environment

The physiology of ion regulation in the highly invasive European green crab Carcinus maenas has been widely studied, but mostly in constant salinity conditions, and not in context of their molt cycle-dependent sternite coloration. The ventral sternites are typically green after molting, and turn red through prolonged intermolt, with a concurrent decrease in stress tolerance. In this study, whole animal and molecular physiology was evaluated at constant low salinity (12), and oscillating salinity (12–32 every 6 h). Performance in three whole animal measures revealed that the green phase is more tolerant than the red phase, and that females are more tolerant than the respective males under both salinity conditions. These differences result from larger increases in expression of the drivers behind ion transport (Na /K -ATPase, cytoplasmic carbonic anhydrase) in green phase and female crabs. Low salinity exposure resulted in increased expression of these markers compared with oscillating salinity, demonstrating that low salinity is more strenuous, as more cellular regulation is required. This agrees with the crabs' natural environmental conditions where prolonged low salinity is rarely experienced. These findings are presented in context of a crab population survey conducted from May 2012 through November 2016 in southern Maine, USA. Female and red phase crabs were found at higher proportions in the intertidal than previously reported. In addition, gravid females were found year round, which is indicative of continuous reproduction. The data demonstrate the necessity to evaluate C. maenas in an ecologically relevant context with respect to color phase within each invasive population to truly understand the invasive capabilities of this species and to better inform management strategies.

Polydiacetylene‐Tb3+ Nanosheets of Which Both the Color and the Fluorescence Can Be Reversibly Switched between Two Colors

Polydiacetylenes (PDAs), an organic layered compound, show a series of intriguing properties, such as thermochromism and fluorescence emission in the red‐phase. However, their irreversible color change, and weak and single‐color fluorescence emitted only from the red‐phase PDAs, have limited their applications. Herein, we report double‐reversible PDA‐Tb3+ nanosheets of which both the color and the fluorescence can be reversibly switched between two colors. PDA‐Tb3+ nanosheets have the nearly defect‐free intercalated structure in which a layer of Tb3+ ions was intercalated in between each two PDA bilayers to tether almost all of the carboxyl groups at the end of the side chains of the PDA. When the PDA is in the blue phase, the PDA‐Tb3+ nanosheets emit the green fluorescence of Tb3+ ions. When the PDA is in the red phase, the Tb3+ fluorescence disappears while the intrinsic red fluorescence of PDA is effectively enhanced through the fluorescence resonance energy transfer (FRET) process; the PDA‐Tb3+ nanosheets emit stronger red fluorescence compared with the PDA in red phase. Moreover, the tethering of almost all of the carboxyl groups at the end of the side chains of the PDA endows the nanosheets with the double reversibility in both the color and fluorescence transitions.

Star-planet interactions

The surface rotations of some red giants are so fast that they must have been spun up by tidal interaction with a close companion, either another star, a brown dwarf, or a planet. We focus here on the case of red giants that are spun up by tidal interaction with a planet. When the distance between the planet and the star decreases, the spin period of the star decreases, the orbital period of the planet decreases, and the reflex motion of the star increases. We study the change rate of these three quantities when the circular orbit of a planet of 15 M$_{J}$ that initially orbits a 2 M$_\odot$ star at 1 au shrinks under the action of tidal forces during the red giant phase. We use stellar evolution models coupled with computations of the orbital evolution of the planet, which allows us to follow the exchanges of angular momentum between the star and the orbit in a consistent way. We obtain that the reflex motion of the red giant star increases by more than 1 m s$^{-1}$ per year in the last $\sim$40 years before the planet engulfment. During this phase, the reflex motion of the star is between 660 and 710 m s$^{-1}$. The spin period of the star increases by more than about 10 minutes per year in the last 3000 y before engulfment. During this period, the spin period of the star is shorter than 0.7 year. During this same period, the variation in orbital period, which is shorter than 0.18 year, is on the same order of magnitude. Changes in reflex-motion and spin velocities are very small and thus most likely out of reach of being observed. The most promising way of detecting this effect is through observations of transiting planets, that is, through{\it } changes of the beginning or end of the transit. A space mission like PLATO might be of great interest for detecting planets that are on the verge of being engulfed by red giants.

Application of central composite design for methyl red dispersive solid phase extraction based on silver nanocomposite hydrogel: Microwave assisted synthesis

In this study microwave irradiation was used to synthesis the silver nanocomposite hydrogel and the usefulness as an adsorbent for the preconcentration, extraction and determination of methyl red (MR) from water by dispersive solid phase extraction method was evaluated. For this purpose, silver nanocomposite hydrogel (SNH) was synthesized and characterized by thermo-gravimetric (TG) analysis, FT-IR, TEM and SEM images. The effects of some important variables such as centrifuge time (min), the pH of the methyl red solution, amount of adsorbent (g), acetone volume (mL) and chloroform volume (mL) on methyl red removal were studied using central composite design (CCD) and the optimum experimental conditions were evaluated by the desirability function (DF) combined response surface methodology (RSM). Under the optimal experimental conditions, the detection limit was found to be 1.4μgmL−1 for MR adsorption. The limit of quantification and the linear range of calibration curve were 4.6μgmL−1 and 0.1–25μgmL−1, respectively.

Estimation of red-light running frequency using high-resolution traffic and signal data

Red-light-running (RLR) emerges as a major cause that may lead to intersection-related crashes and endanger intersection safety. To reduce RLR violations, it’s critical to identify the influential factors associated with RLR and estimate RLR frequency. Without resorting to video camera recordings, this study investigates this important issue by utilizing high-resolution traffic and signal event data collected from loop detectors at five intersections on Trunk Highway 55, Minneapolis, MN. First, a simple method is proposed to identify RLR by fully utilizing the information obtained from stop bar detectors, downstream entrance detectors and advance detectors. Using 12 months of event data, a total of 6550 RLR cases were identified. According to a definition of RLR frequency as the conditional probability of RLR on a certain traffic or signal condition (veh/1000veh), the relationships between RLR frequency and some influential factors including arriving time at advance detector, approaching speed, headway, gap to the preceding vehicle on adjacent lane, cycle length, geometric characteristics and even snowing weather were empirically investigated. Statistical analysis shows good agreement with the traffic engineering practice, e.g., RLR is most likely to occur on weekdays during peak periods under large traffic demands and longer signal cycles, and a total of 95.24% RLR events occurred within the first 1.5s after the onset of red phase. The findings confirmed that vehicles tend to run the red light when they are close to intersection during phase transition, and the vehicles following the leading vehicle with short headways also likely run the red light. Last, a simplified nonlinear regression model is proposed to estimate RLR frequency based on the data from advance detector. The study is expected to helpbetter understand RLR occurrence and further contribute to the future improvement of intersection safety.

The Canonical Luminous Blue Variable AG Car and Its Neighbor Hen 3-519 Are Much Closer than Previously Assumed

Abstract The strong mass loss of Luminous Blue Variables (LBVs) is thought to play a critical role in massive-star evolution, but their place in the evolutionary sequence remains debated. A key to understanding their peculiar instability is their high observed luminosities, which often depends on uncertain distances. Here we report direct distances and space motions of four canonical Milky Way LBVs—AG Car, HR Car, HD 168607, and (candidate) Hen 3-519—from the Gaia first data release. Whereas the distances of HR Car and HD 168607 are consistent with previous literature estimates within the considerable uncertainties, Hen 3-519 and AG Car, both at ∼2 kpc, are much closer than the 6–8 kpc distances previously assumed. As a result, Hen 3-519 moves far from the locus of LBVs on the Hertzsprung–Russell diagram, making it a much less luminous object. For AG Car, considered a defining example of a classical LBV, its lower luminosity would also move it off the S Dor instability strip. Lower luminosities allow both AG Car and Hen 3-519 to have passed through a previous red supergiant phase, lower the mass estimates for their shell nebulae, and imply that binary evolution is needed to account for their peculiarities. These results may also impact our understanding of LBVs as potential supernova progenitors and their isolated environments. Improved distances will be provided in the Gaia second data release, which will include additional LBVs. AG Car and Hen 3-519 hint that this new information may alter our traditional view of LBVs.

Structural dependence of MEH-PPV chromism in solution.

The chromism observed in the MEH-PPV polymer in tetrahydrofuran (THF) solution is discussed as a function of the structural morphology of the backbone chains. To evaluate this phenomenon, we carried out simulations employing a hybrid methodology using molecular dynamics and quantum mechanical approaches. Our results support the hypothesis that the morphological order-disorder transition is related to the change from red to blue phase observed experimentally. The morphological disorder is associated with total or partial twisted arrangements in the polymer backbone, which induces an electronic conjugation length more confined to shorter segments. In addition, the main band of the MEH-PPV UV-Vis spectrum at the lower wavelength is related to the blue phase, in contrast to the red phase found for the more planar backbone chains.

Stagnant Shells in the Vicinity of the Dusty Wolf–Rayet–OB Binary WR 112

Abstract We present high spatial resolution mid-infrared images of the nebula around the late-type carbon-rich Wolf–Rayet (WC)–OB binary system WR 112 taken by the recently upgraded VLT spectrometer and imager for the mid-infrared (VISIR) with the PAH1, Ne ii_2, and Q3 filters. The observations reveal a morphology resembling a series of arc-like filaments and broken shells. Dust temperatures and masses are derived for each of the identified filamentary structures, which exhibit temperatures ranging from K at the exterior W2 filament to K in the central 3″. The total dust mass summed over the features is 2.6 ± 0.4 × 10−5 M ⊙. A multi-epoch analysis of mid-IR photometry of WR 112 over the past ∼20 years reveals no significant variability in the observed dust temperature and mass. The morphology of the mid-IR dust emission from WR 112 also exhibits no significant expansion from imaging data taken in 2001, 2007, and 2016, which disputes the current interpretation of the nebula as a high expansion velocity (∼1200 km s−1) “pinwheel”-shaped outflow driven by the central WC–OB colliding-wind binary. An upper limit of ≲120 km s−1 is derived for the expansion velocity assuming a distance of 4.15 kpc. The upper limit on the average total mass-loss rate from the central 3″ of WR 112 is estimated to be ≲8 × 10−6 M ⊙ year−1. We leave its true nature as an open question, but propose that the WR 112 nebula may have formed in the outflow during a previous red or yellow supergiant phase of the central Wolf–Rayet star.

Effect of Traffic Signal Countdown Timers on Pedestrian Crossings at Signalized Intersection

Installations of signal countdown timers (SCTs) adjacent to the traffic signal heads are on the rise at several intersection locations in India. These SCTs provide information related to the time left for a particular signal phase and thus expected to help the driver take better decision. But no scientific studies were carried out before their installations at intersection locations. Pedestrian countdown timers (PCTs), which work on the same principle as SCTs found to be effective in terms of reducing pedestrian violations, pedestrian-vehicle conflicts as they provide information about the time left for a particular phase. These PCTs are becoming common at urban intersections in Indian cities, but not in very large numbers as their installation will require an additional infrastructural cost. In order to assess whether the SCTs themselves can facilitate the pedestrian movement at signalized intersections or not, the present study attempts to observe their effect on pedestrian movements at zebra crossing locations. When countdown timers were present, a higher percent of the cycles were observed to have some sort of red light violations (RLVs) as compared to the situation when the timer was absence. Average red light violations per red light cycle were found to be 3.2 and 2 RLV/RLV cycle in the presence and absence of signal countdown timers, respectively at intersection 1. The similar trend observed in intersection 2 (6.7 and 2.5 RLV/RLV cycle in the presence and absence of signal countdown timers respectively). SCTs did not have any effect on pedestrian waiting time on curb or pedestrian speed during crossing. These digital timers increased pedestrian violations. In the absence of SCT, less number of pedestrians was observed to cross the road during green and yellow phase, whereas higher number of pedestrian crossings was found during the initial portion of red phase. Overall, it was observed that rampant installation of these SCTs at major urban signalized intersections without conducting extensive studies would detrimentally affect the pedestrian movements making the crossing process complex and unsafe.