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G. Ramachandran

Publications and source records attributed to G. Ramachandran.

At least 19 recordsLinked to original sources
arXiv2024

Malicious Package Detection using Metadata Information

Protecting software supply chains from malicious packages is paramount in the evolving landscape of software development. Attacks on the software supply chain involve attackers injecting harmful software into commonly used packages or libraries in a software repository. For instance, JavaScript uses Node Package Manager (NPM), and Python uses Python Package Index (PyPi) as their respective package repositories. In the past, NPM has had vulnerabilities such as the event-stream incident, where a malicious package was introduced into a popular NPM package, potentially impacting a wide range of projects. As the integration of third-party packages becomes increasingly ubiquitous in modern software development, accelerating the creation and deployment of applications, the need for a robust detection mechanism has become critical. On the other hand, due to the sheer volume of new packages being released daily, the task of identifying malicious packages presents a significant challenge. To address this issue, in this paper, we introduce a metadata-based malicious package detection model, MeMPtec. This model extracts a set of features from package metadata information. These extracted features are classified as either easy-to-manipulate (ETM) or difficult-to-manipulate (DTM) features based on monotonicity and restricted control properties. By utilising these metadata features, not only do we improve the effectiveness of detecting malicious packages, but also we demonstrate its resistance to adversarial attacks in comparison with existing state-of-the-art. Our experiments indicate a significant reduction in both false positives (up to 97.56%) and false negatives (up to 91.86%).

cs.CR↗
arXiv2019

Statistical Assemblies of Particles with Spin

Spin, $s$ in quantum theory can assume only half odd integer or integer values. For a given $s$, there exist $n=2s+1$ states $|s,m\rangle$, $m=s,s-1,........,-s$. A statistical assembly of particles (like a beam or target employed in experiments in physics) with the lowest value of spin $s=\frac {1}{2}$ can be described in terms of probabilities $p_m$ assigned to the two states $m=\pm \frac {1}{2}$. A generalization of this concept to higher spins $s>\frac {1}{2}$ leads only to a particularly simple category of statistical assemblies known as `Oriented systems'. To provide a comprehensive description of all realizable categories of statistical assemblies in experiments, it is advantageous to employ the generators of the Lie group $SU(n)$. The probability domain then gets identified to the interior of regular polyhedra in $\Re^{n-1},$ where the centre corresponds to an unpolarized assembly and the vertices represent `pure' states. All the other interior points correspond to `mixed' states. The higher spin system has embedded within itself a set of $s(2s+1)$ independent axes, which are determinable empirically. Only when all these axes turn out to be collinear, the simple category of `Oriented systems' is realized, where probabilities $p_m$ are assigned to the states $|s,m\rangle$. The simplest case of higher spin $s=1$ provides an illustrative example, where additional features of `aligned' and more general `non oriented' categories are displayed.

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arXiv2019

$Δ$ Contribution to $ pp \to ppπ^0$

A model independent discussion of $Δ-$production in $pp \to pp π^0$ is presented and the $Δ-$contributions to the 16 $pp \to ppπ^0$ partial wave amplitudes are identified taking the $Ds$ and $Sd$ channels also into consideration.

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arXiv2012

Photodisintegration of aligned deuterons at astrophysical energies using linearly polarized photons

Following the model independent approach to deuteron photodisintegration with linearly polarized $γ-$rays, we show that the measurements of the tensor analyzing powers on aligned deuterons along with the differential cross section involve five different linear combinations of the isovector $E1^j_v; j=0,1,2$ amplitudes interfering with the isoscalar $M1_s$ and $E2_s$ amplitudes. This is of current interest in view of the recent experimental finding \cite{blackston1} that the three $E1^j_v$ amplitudes are distinct and also the reported experimental observation \cite{sawatzky} on the front-back (polar angle) asymmetry in the differential cross section.

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arXiv2011

Deuteron photodisintegration with polarized lasers

A model independent theoretical analysis of recent experimental data on deuteron photodisintegration with polarized laser beams is presented. We find that it is important to distinguish between the three isovector E1 amplitudes $E1_v^j$ in reaction channels with total angular momentum $j=0,1,2$ and that the isoscalar M1 amplitude $M1_s$ is non-zero in the photon energy range $3.5 MeV < E_γ< 10 MeV$

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arXiv2010

Phase ambiguity of the threshold amplitude in pp -> ppπ^0

Measurements of spin observables in pp -> {\vec p}{\vec p}π^0 are suggested to remove the phase ambiguity of the threshold amplitude. The suggested measurements complement the IUCF data on {\vec p}{\vec p} -> ppπ^0 to completely determine all the twelve partial wave amplitudes, taken into consideration by Mayer et.al. [15] and Deepak, Haidenbauer and Hanhart [20].

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arXiv2009

Final state polarization of protons in $pp \to pp ω$

Model independent formulae are derived for the polarizations and spin correlations of protons in the final state of $pp \to ppω$, taking into consideration all the six threshold partial wave amplitudes $f_1, ..., f_6$ covering $Ss, Sp$ and $Ps$ channels. It is shown that these measurements of the final state spin observables, employing only an unpolarized beam and an unpolarized target, may be utilized to complement measurements, at the double differential level, suggested earlier [Phys. Rev. \textbf{C78}, 01210(R)(2009)] so that all the six partial wave amplitudes may be determined empirically.

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arXiv2009

Decay of Polarized Delta

The resonance $Δ(1232)$ with spin-parity ${3 \over 2}^+$, which contributes dominantly to the reactions like $γN \to πN$ and $NN \to NNπ$ at intermediate energies, may be expected to be produced in characteristically different polarized spin states. As such an analysis of the decay of polarized delta is presented, which may be utilized to probe empirically the production mechanism. It is shown that measurements of the angular distributions of the pion and the polarization of the nucleon arising out of ${\vecΔ}$ decay can determine empirically the Fano statistical tensors characterizing the ${\vecΔ}$.

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arXiv2008

Polarization phase matrices for radiation scattering on atoms in external magnetic fields: The case of forbidden transitions in astrophysics

Using a quantum electrodynamical approach, we derive the scattering phase matrices for polarized radiation involving forbidden line transitions and in the presence of an external magnetic field. The case of (J=0->2->0) scattering is considered as an example. The non-magnetic Rayleigh scattering phase matrix is also presented. The Stokes profiles in a single scattering event are computed for the strong field (Zeeman) and weak field (Hanle) limits, covering also the regime of intermediate field strengths (Hanle- Zeeman).

astro-ph↗
arXiv2008

Omega meson production in pp collisions with a polarized beam

Model independent formulae are derived for the beam analyzing power $A_y$ and beam to meson spin transfers in $pp \to pp ω$ taking into consideration all the six threshold partial wave amplitudes covering the $Ss, Sp$ and $Ps$ channels. Attention is also focussed on the empirical determination of the lowest three partial wave amplitudes $f_1, f_2, f_3$ without any discrete ambiguities.

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arXiv2007

Scattering Polarization in the Presence of Magnetic and Electric Fields

The polarization of radiation by scattering on an atom embedded in combined external quadrupole electric and uniform magnetic fields is studied theoretically. Limiting cases of scattering under Zeeman effect and Hanle effect in weak magnetic fields are discussed. The theory is general enough to handle scattering in intermediate magnetic fields (Hanle-Zeeman effect) and for arbitrary orientation of magnetic field. The quadrupolar electric field produces asymmetric line shifts and causes interesting level-crossing phenomena either in the absence of an ambient magnetic field or in its presence. It is shown that the quadrupolar electric field produces an additional depolarization in the $Q/I$ profiles and rotation of the plane of polarization in the $U/I$ profile over and above that arising from magnetic field itself. This characteristic may have a diagnostic potential to detect steady state and time varying electric fields that surround radiating atoms in Solar atmospheric layers.

astro-ph↗
arXiv2007

Irreducible tensor approach to spin observables in photo production of mesons with arbitrary spin-parity $s^π$

A theoretical formalism leading to elegant derivation of formulae for all spin observables is outlined for photo production of mesons with arbitrary spin parity $s^π$. The salient features of this formalism based on irreducible tensor techniques are i) the number of independent irreducible tensor amplitudes is $4(2s+1)$, ii) a single compact formula is sufficient to express these amplitudes in terms of allowed electric and magnetic multipole amplitudes and iii) all the spin observables including beam analyzing powers as well as the differential cross section are expressible in terms of bilinear irreducible tensors of rank 0 to $2(s+1)$. The relationship between the irreducible tensor amplitudes and the helicity amplitudes is elucidated in general and explicit expressions for the helicity amplitudes are given in terms of the irreducible tensor amplitudes in the particular cases of pseudoscalar and vector meson photo production. The connection between the irreducible tensor amplitudes introduced here and the well known CGLN amplitudes for photo production of pseudoscalar mesons is also established.

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arXiv2006

Deuteron photodisintegration with polarized photons at astrophysical energies

Following precise experimental studies at the Duke Free-Electron Laser Laboratory, we discuss photodisintegration of deuterons with 100% linearly polarized photons using a model independent theoretical approach taking together $M1$ and $E1$ amplitudes simultaneously. The isoscalar $M1_s$ contribution is also taken exactly into account. From the existing experimental measurement on doubly polarized thermal neutron capture, it is seen that the isoscalar $M1_s$ contribution could be of the same order of magnitude as the experimentally measured cross sections at energies relevant to Big Bang Nucleosynthesis (BBN). Therefore appropriate measurements on deuteron photodisintegration are suggested to empirically determine the $M1_s$ contribution at astrophysical energies.

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arXiv2005

Scattering of Polarized Radiation by Atoms in Magnetic and Electric Fields

The polarization of radiation by scattering on an atom embedded in combined external quadrupole electric and uniform magnetic fields is studied theoretically. Analytic formulae are derived for the scattering phase matrix. Limiting cases of scattering under Zeeman effect, and Hanle effect in weak magnetic fields are discussed.

astro-ph↗
arXiv2005

Omega Production in pp Collisions

A model-independent irreducible tensor formalism which has been developed earlier to analyze measurements of $\vec{p}\vec{p}\to pp π^\circ$, is extended to present a theoretical discussion of $\vec{p}\vec{p}\to pp ω$ and the polarization of $ω$ in $pp\to pp \vecω$. The recent measurement of unpolarized differential cross section for $pp\to pp ω$ is analyzed using this theoretical formalism.

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arXiv2002

Radiative capture of polarized neutrons by polarized protons

A model-independent irreducible tensor approach to p(n,gamma)d is presented and an explicit form for the spin-structure of the matrix for the reaction is obtained in terms of the Pauli spin-matrices for the neutron and the proton. Expressing the multipole amplitudes in terms of the triplet --> triplet and singlet --> triplet transitions, we point out how the initial singlet and triplet contributions to the differential cross section can be determined empirically.

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