arXiv subjects

Dipankar Das

Publications and source records attributed to Dipankar Das.

101 records · Page 6Linked to original sources

arXiv2014

Identifying Bengali Multiword Expressions using Semantic Clustering

One of the key issues in both natural language understanding and generation is the appropriate processing of Multiword Expressions (MWEs). MWEs pose a huge problem to the precise language processing due to their idiosyncratic nature and diversity in lexical, syntactical and semantic properties. The semantics of a MWE cannot be expressed after combining the semantics of its constituents. Therefore, the formalism of semantic clustering is often viewed as an instrument for extracting MWEs especially for resource constraint languages like Bengali. The present semantic clustering approach contributes to locate clusters of the synonymous noun tokens present in the document. These clusters in turn help measure the similarity between the constituent words of a potentially candidate phrase using a vector space model and judge the suitability of this phrase to be a MWE. In this experiment, we apply the semantic clustering approach for noun-noun bigram MWEs, though it can be extended to any types of MWEs. In parallel, the well known statistical models, namely Point-wise Mutual Information (PMI), Log Likelihood Ratio (LLR), Significance function are also employed to extract MWEs from the Bengali corpus. The comparative evaluation shows that the semantic clustering approach outperforms all other competing statistical models. As a by-product of this experiment, we have started developing a standard lexicon in Bengali that serves as a productive Bengali linguistic thesaurus.

cs.CL↗

arXiv2013

Scalar sector properties of two-Higgs-doublet models with a global U(1) symmetry

We analyze the scalar sector properties of a general class of two-Higgs-doublet models which has a global U(1) symmetry in the quartic terms. We find constraints on the parameters of the potential from the considerations of unitarity of scattering amplitudes, the global stability of the potential and the $ρ$-parameter. We concentrate on the spectrum of the non-standard scalar masses in the decoupling limit which is preferred by the Higgs data at the LHC. We exhibit charged-Higgs induced contributions to the diphoton decay width of the 125\,GeV Higgs boson and its correlation with the corresponding $Zγ$ width.

hep-ph↗

arXiv2013

High precision measurement of ultraweak transitions of the a${^1}{\triangle}_g{\leftarrow}$X $^3Σ^{-}_g$ $(0,0)$ band of molecular oxygen

We have used a highly sensitive cavity-enhanced frequency modulation spectroscopy technique to measure different parameters of the ultraweak transitions of a${^1}{\triangle}_g{\leftarrow}$X $^3Σ^{-}_g$ $(0,0)$ band of molecular oxygen in the range 7640 cm$^{-1}$ to 7917 cm$^{-1}$. The self-broadened half-width and air-broadened half-width of the transitions have been measured for three different pressures for both $^{16}$O$_2$ and $^{18}$O$_2$. To measure the line intensity and self-broadened half-width we have used ultra pure oxygen sample and air-broadened half-width was measured with dry air sample. The $(0,0)$ band of $^{16}$O$_2$ and $^{18}$O$_2$ show weak quadrupole transitions with line intensities ranging from $1\times10^{-30}$ to $1.9\times10^{-28}$ cm/molecule. The measurements are in excellent agreement with the recent measurement of Rothman et. al

physics.optics↗

arXiv2013

Modified Higgs couplings and unitarity violation

Prompted by the recent observation of a Higgs-like particle at the CERN Large Hadron Collider (LHC), we investigate a quantitative correlation between possible departures of the gauge and Yukawa couplings of this particle from their Standard Model expectations and the scale of unitarity violation in the processes $WW \to WW$ and $t\bar t \to WW$.

hep-ph↗

arXiv2010

Very long optical path-length from a compact multi-pass cell

The multiple-pass optical cell is an important tool for laser absorption spectroscopy and its many applications. For most practical applications, such as trace-gas detection, a compact and robust design is essential. Here we report an investigation into a multi-pass cell design based on a pair of cylindrical mirrors, with a particular focus on achieving very long optical paths. We demonstrate a path-length of 50.31 m in a cell with 40 mm diameter mirrors spaced 88.9 mm apart - a 3-fold increase over the previously reported longest path-length obtained with this type of cell configuration. We characterize the mechanical stability of the cell and describe the practical conditions necessary to achieve very long path-lengths.

physics.optics↗

arXiv2010

High-precision measurement of hyperfine structure in the $D$ lines of alkali atoms

We have measured hyperfine structure in the first-excited $P$ state ($D$ lines) of all the naturally-occurring alkali atoms. We use high-resolution laser spectroscopy to resolve hyperfine transitions, and measure intervals by locking the frequency shift produced by an acousto-optic modulator to the difference between two transitions. In most cases, the hyperfine coupling constants derived from our measurements improve previous values significantly.

physics.atom-ph↗

arXiv2003

Precise measurements of UV atomic lines: Hyperfine structure and isotope shifts in the 398.8 nm line of Yb

We demonstrate a technique for frequency measurements of UV transitions with sub-MHz precision. The frequency is measured using a ring-cavity resonator whose length is calibrated against a reference laser locked to the $D_2$ line of $^{87}$Rb. We have used this to measure the 398.8 nm ${^1S}_0 \leftrightarrow {^1P}_1$ line of atomic Yb. We report isotope shifts of all the seven stable isotopes, including the rarest isotope $^{168}$Yb. We have been able to resolve the overlapping $^{173}$Yb($F = 3/2$) and $^{172}$Yb transitions for the first time. We also obtain high-precision measurements of excited-state hyperfine structure in the odd isotopes, $^{171}$Yb and $^{173}$Yb. The measurements resolve several discrepancies among earlier measurements.

physics.atom-ph↗

arXiv2003

Precise frequency measurements of atomic transitions using a Rb-stabilized resonator

We demonstrate a technique for frequency measurements of atomic transitions with a precision of 30 kHz. The frequency is measured using a ring-cavity resonator whose length is calibrated against a reference laser locked to the $D_2$ line of $^{87}$Rb, the frequency of which is known to 10 kHz. We have used this to measure the hyperfine structure in the $5P_{3/2}$ state of $^{85}$Rb. We obtain precise values for the hyperfine constants $A=25.041(6)$ MHz and $B=26.013(25)$ MHz, and a value of 77.992(20) MHz for the isotope shift in the $D_2$ line.

physics.atom-ph↗

arXiv2002

Precise fine-structure and hyperfine-structure measurements in Rb

We demonstrate a new technique for measuring the absolute frequencies of atomic transitions. The technique uses a ring-cavity resonator whose length is calibrated using a reference laser locked to the D_2 line in {87}Rb. The frequency of this line is known to be 384 230 484.468(10) MHz. Using a second laser locked to the D_1 line of Rb, we measure the frequencies of various hyperfine transitions in the D_1 and D_2 lines with a precision of 30 kHz. We obtain the following values: 120.687(17) MHz and 406.520(25) MHz for the 5P_{1/2} hyperfine constant A in {85}Rb and {87}Rb; 377 107 385.623(50) MHz and 377 107 463.209(50) MHz for the D_1 line in {85}Rb and {87}Rb; and 384 230 406.528(50) MHz for the D_2 line in {85}Rb. This yields the fine-structure interval and the isotope shifts. The precision obtained is a significant improvement over previous measurements.

physics.atom-ph↗

arXiv2002

Precise frequency measurements of the D-lines and fine-structure interval in K

We use a diode laser locked to a Rb transition as the frequency reference along with a scanning Michelson interferometer to make precise measurements on the $D_1$ and $D_2$ lines of potassium. The Rb reference frequency is known with sub-MHz accuracy. We obtain the following values for the energy levels: 12 985.169 60(13)(15) cm$^{-1}$ for the $4P_{1/2}$ state ($D_1$ line); 13 042.875 95(14)(15) cm$^{-1}$ for the $4P_{3/2}$ state ($D_2$ line); and 57.706 35(19)(15) cm$^{-1}$ for the $4P_{3/2}-4P_{1/2}$ fine-structure interval. The leading source of systematic error cancels in the determination of the interval. The errors represent about an order of magnitude improvement over tabulated values.

physics.atom-ph↗

arXiv2002

Frequency locking of tunable diode lasers to a stabilized ring-cavity resonator

We demonstrate a technique for locking the frequency of a tunable diode laser to a ring-cavity resonator. The resonator is stabilized to a diode laser which is in turn locked to an atomic transition, thus giving it absolute frequency calibration. The ring-cavity design has the principal advantage that there is no feedback destabilization of the laser. The cavity has a free-spectral range of 1.3 GHz and $Q$ of about 35, which gives robust locking of the laser. The locked laser is able to track large scans of the cavity.

physics.optics↗