Ahsan Zafar - Academia.edu (original) (raw)

Papers by Ahsan Zafar

Experimental studies of power converters rectifiers, their performance with different loads and t... more Experimental studies of power converters rectifiers, their performance with different loads and their analysis is included in this research. These results are laboratory based in which controlled and uncontrolled rectification (FW, 1-& 3-) are observed with different loads (R, R-L) with their output rectified waveforms. Software models are developed, bases on the attained parameters in order to compare their precision with laboratory models and the final harmonics and total harmonic distortion produced by the power rectifier converters due to non linear loads are concluded.

Proceedings of the 2021 ACM Asia Conference on Computer and Communications Security

Targeted advertisement is prevalent on the Web. Many privacyenhancing tools have been developed t... more Targeted advertisement is prevalent on the Web. Many privacyenhancing tools have been developed to thwart targeted advertisement. Adblock Plus is one such popular tool, used by millions of users on a daily basis, to block unwanted ads and trackers. Adblock Plus uses EasyList and EasyPrivacy, the most prominent and widely used open-source filters, to block unwanted web contents. However, Adblock Plus, by default, also enables an exception list to unblock web requests that comply with specific guidelines defined by the Acceptable Ads Committee. Any publisher can enroll into the Acceptable Ads initiative to request the unblocking of web contents. Adblock Plus in return charges a licensing fee from large entities, who gain a significant amount of ad impressions per month due to participation in the Acceptable Ads initiative. However, the privacy implications of the default inclusion of the exception list has not been well studied, especially as it can unblock not only ads, but also trackers (e.g., unblocking contents otherwise blocked by EasyPrivacy). In this paper, we take a data-driven approach, where we collect historical updates made to Adblock Plus's exception list and real-world web traffic by visiting the top 10k websites listed by Tranco. Using such data we analyze not only how the exception list has evolved over the years in terms of both contents unblocked and partners/entities enrolled into the Acceptable Ads initiative, but also the privacy implications of enabling the exception list by default. We found that Google not only unblocks the most number of unique domains, but is also unblocked by the most number of unique partners. From our traffic analysis, we see that of the 42,210 Google bound web requests, originally blocked by EasyPrivacy, around 80% of such requests are unblocked by the exception list. More worryingly, many of the requests enable 1-by-1 tracking pixel

Analytical Chemistry, 1996

The complexation reactions of beryllium(II) ion with 1-(2,4-dihydroxy-1-phenylazo)-8-hydroxy-3,6-... more The complexation reactions of beryllium(II) ion with 1-(2,4-dihydroxy-1-phenylazo)-8-hydroxy-3,6-naphthalenedisulfonate (H-resorcinol) are studied. The acid dissociation constants of H-resorcinol, H(3)L(2-), at 293 K and I = 0.10 [K(OH, NO(3))] are pK(a)((1)) = 5.67, pK(a)((2)) = 8.57, and pK(a)((3)) > 13. The formation constant at 293 K and I = 0.10 [(K,H)NO(3)] is estimated to be log[{[Be(HL)(2-)][H(+)](2)}/{[Be][H(3)L(2-)]}] = -4.58, and pK(a)' = 6.39 for [Be(HL)](2-), which give the basis for the optimization of the precolumn chelation reactions and the masking system with EDTA. The kinetic data for ligand substitution reactions with sulfosalicylate ion are also reported to demonstrate the remarkable inertness of the Be chelate, which is suitable for HPLC separation. Reported is an accurate method for determining traces of Be(II) ion at nanomolar levels with photometric detection coupled with ion-pair reversed-phase HPLC. The chelate, [Be(II)L](3-), is efficiently separated on an Asahipak ODP-50 column using tetrabutylammonium bromide as an ion-pairing agent in a methanol (35 wt %)-water eluent. Only Al and Fe give peaks under the conditions used. The large molar absorptivity of the H-resorcinol chelate, 3.99 × 10(4) M(-1) cm(-1) at 500 nm, and the short retention time with excellent peak resolution ensure the ultralow detection limit (3σ blank) down to 7.2 ppt (0.8 nM) with no preconcentration procedures. The excellent toughness toward the matrix influence was demonstrated using the model solution for an air-dust sample. The HPLC separation, coupled with the EDTA masking procedure, enables one to detect Be(II) ion at 20 nM in the presence of metals at the natural abundance levels in air samples, such as Al, Fe, Ca, Mg, Zn, and Pb at 240, 140, 300, 66, 16, and 6.2 μM, respectively, in the final solution.

Experimental studies of power converters rectifiers, their performance with different loads and t... more Experimental studies of power converters rectifiers, their performance with different loads and their analysis is included in this research. These results are laboratory based in which controlled and uncontrolled rectification (FW, 1-& 3-) are observed with different loads (R, R-L) with their output rectified waveforms. Software models are developed, bases on the attained parameters in order to compare their precision with laboratory models and the final harmonics and total harmonic distortion produced by the power rectifier converters due to non linear loads are concluded.

Proceedings of the 2021 ACM Asia Conference on Computer and Communications Security

Targeted advertisement is prevalent on the Web. Many privacyenhancing tools have been developed t... more Targeted advertisement is prevalent on the Web. Many privacyenhancing tools have been developed to thwart targeted advertisement. Adblock Plus is one such popular tool, used by millions of users on a daily basis, to block unwanted ads and trackers. Adblock Plus uses EasyList and EasyPrivacy, the most prominent and widely used open-source filters, to block unwanted web contents. However, Adblock Plus, by default, also enables an exception list to unblock web requests that comply with specific guidelines defined by the Acceptable Ads Committee. Any publisher can enroll into the Acceptable Ads initiative to request the unblocking of web contents. Adblock Plus in return charges a licensing fee from large entities, who gain a significant amount of ad impressions per month due to participation in the Acceptable Ads initiative. However, the privacy implications of the default inclusion of the exception list has not been well studied, especially as it can unblock not only ads, but also trackers (e.g., unblocking contents otherwise blocked by EasyPrivacy). In this paper, we take a data-driven approach, where we collect historical updates made to Adblock Plus's exception list and real-world web traffic by visiting the top 10k websites listed by Tranco. Using such data we analyze not only how the exception list has evolved over the years in terms of both contents unblocked and partners/entities enrolled into the Acceptable Ads initiative, but also the privacy implications of enabling the exception list by default. We found that Google not only unblocks the most number of unique domains, but is also unblocked by the most number of unique partners. From our traffic analysis, we see that of the 42,210 Google bound web requests, originally blocked by EasyPrivacy, around 80% of such requests are unblocked by the exception list. More worryingly, many of the requests enable 1-by-1 tracking pixel

Analytical Chemistry, 1996

The complexation reactions of beryllium(II) ion with 1-(2,4-dihydroxy-1-phenylazo)-8-hydroxy-3,6-... more The complexation reactions of beryllium(II) ion with 1-(2,4-dihydroxy-1-phenylazo)-8-hydroxy-3,6-naphthalenedisulfonate (H-resorcinol) are studied. The acid dissociation constants of H-resorcinol, H(3)L(2-), at 293 K and I = 0.10 [K(OH, NO(3))] are pK(a)((1)) = 5.67, pK(a)((2)) = 8.57, and pK(a)((3)) > 13. The formation constant at 293 K and I = 0.10 [(K,H)NO(3)] is estimated to be log[{[Be(HL)(2-)][H(+)](2)}/{[Be][H(3)L(2-)]}] = -4.58, and pK(a)' = 6.39 for [Be(HL)](2-), which give the basis for the optimization of the precolumn chelation reactions and the masking system with EDTA. The kinetic data for ligand substitution reactions with sulfosalicylate ion are also reported to demonstrate the remarkable inertness of the Be chelate, which is suitable for HPLC separation. Reported is an accurate method for determining traces of Be(II) ion at nanomolar levels with photometric detection coupled with ion-pair reversed-phase HPLC. The chelate, [Be(II)L](3-), is efficiently separated on an Asahipak ODP-50 column using tetrabutylammonium bromide as an ion-pairing agent in a methanol (35 wt %)-water eluent. Only Al and Fe give peaks under the conditions used. The large molar absorptivity of the H-resorcinol chelate, 3.99 × 10(4) M(-1) cm(-1) at 500 nm, and the short retention time with excellent peak resolution ensure the ultralow detection limit (3σ blank) down to 7.2 ppt (0.8 nM) with no preconcentration procedures. The excellent toughness toward the matrix influence was demonstrated using the model solution for an air-dust sample. The HPLC separation, coupled with the EDTA masking procedure, enables one to detect Be(II) ion at 20 nM in the presence of metals at the natural abundance levels in air samples, such as Al, Fe, Ca, Mg, Zn, and Pb at 240, 140, 300, 66, 16, and 6.2 μM, respectively, in the final solution.