833 research outputs found
Discovery of Blue Luminescence in the Red Rectangle: Possible Fluorescence from Neutral Polycyclic Aromatic Hydrocarbon Molecules?
Here we report our discovery of a band of blue luminescence (BL) in the Red
Rectangle (RR) nebula. This enigmatic proto-planetary nebula is also one of the
brightest known sources of extended red emission as well as of unidentified
infra-red (UIR) band emissions. The spectrum of this newly discovered BL is
most likely fluorescence from small neutral polycyclic aromatic hydrocarbon
(PAH) molecules. PAH molecules are thought to be widely present in many
interstellar and circumstellar environments in our galaxy as well as in other
galaxies, and are considered likely carriers of the UIR-band emission. However,
no specific PAH molecule has yet been identified in a source outside the solar
system, as the set of mid-infra-red emission features attributed to these
molecules between the wavelengths of 3.3 micron and 16.4 micron is largely
insensitive to molecular sizes. In contrast, near-UV/blue fluorescence of PAHs
is more specific as to size, structure, and charge state of a PAH molecule. If
the carriers of this near-UV/blue fluorescence are PAHs, they are most likely
neutral PAH molecules consisting of 3-4 aromatic rings such as anthracene
(C14H10) and pyrene (C16H10). These small PAHs would then be the largest
molecules specifically identified in the interstellar medium.Comment: 4 pages, 4 figures, Accepted for publication in ApJL (LaTeX, uses
emulateapj.sty
Infrared Period-Luminosity Relations of Evolved Variable Stars in the Large Magellanic Cloud
We combine variability information from the MAssive Compact Halo Objects
(MACHO) survey of the Large Magellanic Cloud (LMC) with infrared photometry
from the Spitzer Space Telescope Surveying the Agents of a Galaxy's Evolution
(SAGE) survey to create a dataset of ~30 000 variable red sources. We
photometrically classify these sources as being on the first ascent of the Red
Giant Branch (RGB), or as being in one of three stages along the Asymptotic
Giant Branch (AGB): oxygen-rich, carbon-rich, or highly reddened with
indeterminate chemistry ("extreme" AGB candidates). We present linear
period-luminosity relationships for these sources using 8 separate infrared
bands (J, H, K, 3.6, 4.5, 5.8, 8.0, and 24 micron) as proxies for the
luminosity. We find that the wavelength dependence of the slope of the
period-luminosity relationship is different for different photometrically
determined classes of AGB stars. Stars photometrically classified as O-rich
show the least variation of slope with wavelength, while dust enshrouded
extreme AGB stars show a pronounced trend toward steeper slopes with increasing
wavelength. We find that O-rich AGB stars pulsating in the fundamental mode
obey a period-magnitude relation with a slope of -3.41 +/- 0.04 when magnitude
is measured in the 3.6 micron band, in contrast to C-rich AGB stars, which obey
a relation of slope -3.77 +/- 0.05
TWEEN CONSUMERS : A STUDY OF THE IMPACT OF SOCIAL MEDIA ON TWEEN'S BUYING DECISIONS
ABSTRACT
The communication channel of Social Media is one of the most revolutionary developments of technology. The fact that consumers use Social Media actively to gather information about the products they have to purchase, has already been well established. Consumers have the power to influence other buyers, through reviews on social media, making social media marketing a critical component of the marketing mix of any company.
This paper conducts an exploratory study of the impact of Social Media on the buying decision making process of Tween Consumers, a subset of the Z generation, (Williams, Page, Petrosky & Hernandez, 2009). Tweens are young consumers, in the age of 9-14years, a segment that is fast emerging as extremely attractive to marketers due to its typical characteristics. These highly brand conscious, digital natives are powerful influencers in the family buying decisions and constitute the segment that will be the future market as well as the purchase decision makers of tomorrow. Designing an effective marketing mix and communication strategy for the tweens is a challenge since this target group is full of dichotomies. These impulsive buyers have access to a lot of information online and connect with peers on Social Media, but the final decision makers are still the parents.
For this study, a structured, predesigned questionnaire was administered to 81 tweens in the cites of Mumbai and Delhi via convenience sampling. Based on the findings of the survey, marketers should target both parents and tweens in order to develop effective social marketing and communication strategies.
KEYWORDS : Tweens, social media, buying decisions, consumer behavior ,brand awareness, Gen Z , Gen
Diagnostics for specific PAHs in the far-IR: searching neutral naphthalene and anthracene in the Red Rectangle
Context. In the framework of the interstellar polycyclic aromatic
hydrocarbons (PAHs) hypothesis, far-IR skeletal bands are expected to be a
fingerprint of single species in this class. Aims. We address the question of
detectability of low energy PAH vibrational bands, with respect to spectral
contrast and intensity ratio with ``classical'' Aromatic Infrared Bands (AIBs).
Methods. We extend our extablished Monte-Carlo model of the photophysics of
specific PAHs in astronomical environments, to include rotational and
anharmonic band structure. The required molecular parameters were calculated in
the framework of the Density Functional Theory. Results. We calculate the
detailed spectral profiles of three low-energy vibrational bands of neutral
naphthalene, and four low-energy vibrational bands of neutral anthracene. They
are used to establish detectability constraints based on intensity ratios with
``classical'' AIBs. A general procedure is suggested to select promising
diagnostics, and tested on available Infrared Space Observatory data for the
Red Rectangle nebula. Conclusions. The search for single, specific PAHs in the
far-IR is a challenging, but promising task, especially in view of the
forthcoming launch of the Herschel Space Observatory.Comment: 13 pages, 13 figures, accepted for publication in A&
Recommended from our members
Nanodielectics (A "Universal" Panacea for Solving All Electrical Insualation Problems?)
This text summarizes the keynote presentation that is based on the full-length paper of the same title. Dr. FreÌchette's oral presentation should not be seen as a summary of the âBrainstorm paperâ but a glance at some major accomplishments, hinrances and still remaining questions relative to nanodielectrics. Are nanodielectrics a âuniversalâ panacea? The answer to that question is no - but they've got a lot of potential
Electronic spectroscopy of medium-sized polycyclic aromatic hydrocarbons: Implications for the carriers of the 2175 {\AA} UV bump
Mixtures of polycylic aromatic hydrocarbons (PAHs) have been produced by
means of laser pyrolysis. The main fraction of the extracted PAHs were
primarily medium-sized, up to a maximum size of 38 carbon atoms per molecule.
The use of different extraction solvents and subsequent chromatographic
fractionation provided mixtures of different size distributions. UV-VIS
absorption spectra have been measured at low temperature by matrix isolation
spectroscopy and at room temperature with PAHs as film-like deposits on
transparent substrates. In accordance with semi-empirical calculations, our
findings suggest that large PAHs with sizes around 50 to 60 carbon atoms per
molecule could be responsible for the interstellar UV bump at 217.5 nm.Comment: 6 pages, 4 Postscript figures, published in Astrophys. J. Lett.
(2010
- âŠ