Kadar Unsur Timbal pada Tanaman Kangkung di Tiga Pasar Tradisional Kecamatan Cilandak, Jakarta Selatan

Water spinach (Ipomoea sp.) is a plant that is commonly consumed by the public. Shifting cultivation, distribution and sales that are not protected make vegetables easily contaminated by pollutants in the environment, one of the lead element. This study was conducted to determine the element content of Pb in water spinach sold in three traditional markets Cilandak subdistrict, South Jakarta. This study was conducted from February-March 2014 by using Atomic Absorption Spectrophotometer instrument (AAS) method flame. Analysis of the data using Analysis of Variance (ANOVA) with a confidence level of 95 %. If there are any differences, then followed by Duncan's Multiple Range Test. The Maximum Tolerable Intake (MTI) test to determine the maximal consumption of watercress with a particular assay with an approximate weight of 60 kg. Based on this research, the element content of lead in water spinach in three traditional markets District of Cilandak ranged from 1.22 to 22.06 mg/kg. No significant effect on the three traditional markets District of Cilandak location. Organ roots have high levels of lead element compared to levels in the leaves and stems. The entire test sample had levels of lead element above SNI 7387:2009 maximum threshold of 0.5 mg/kg so They are not safe for consumption. Average maximum weight of kale on the three traditional markets in Sub Cilandak that may be consumed per week in the organs of leaves and stems ranged from 0.1492 to 0.6032 kg

Opportunities and limitations of transition voltage spectroscopy: a theoretical analysis

In molecular charge transport, transition voltage spectroscopy (TVS) holds the promise that molecular energy levels can be explored at bias voltages lower than required for resonant tunneling. We investigate the theoretical basis of this novel tool, using a generic model. In particular, we study the length dependence of the conducting frontier orbital and of the 'transition voltage' as a function of length. We show that this dependence is influenced by the amount of screening of the electrons in the molecule, which determines the voltage drop to be located at the contacts or across the entire molecule. We observe that the transition voltage depends significantly on the length, but that the ratio between the transition voltage and the conducting frontier orbital is approximately constant only in strongly screening (conjugated) molecules. Uncertainty about the screening within a molecule thus limits the predictive power of TVS. We furthermore argue that the relative length independence of the transition voltage for non-conjugated chains is due to strong localization of the frontier orbitals on the end groups ensuring binding of the rods to the metallic contacts. Finally, we investigate the characteristics of TVS in asymmetric molecular junctions. If a single level dominates the transport properties, TVS can provide a good estimate for both the level position and the degree of junction asymmetry. If more levels are involved the applicability of TVS becomes limited.Comment: 8 pages, 12 figure

Charge Transport Across Insulating Self-Assembled Monolayers: Non-equilibrium Approaches and Modeling To Relate Current and Molecular Structure

This paper examines charge transport by tunneling across a series of electrically insulating molecules with the structure HS(CH2)4CONH(CH2)2R) in the form of self-assembled monolayers (SAMs), supported on silver. The molecules examined were studied experimentally by Yoon et al. (Angew. Chem. Int. Ed. 2012, 51, 4658–4661), using junctions of the structure AgS(CH2)4CONH(CH2)2R//Ga2O3/EGaIn. The tail group R had approximately the same length for all molecules, but a range of different structures. Changing the R entity over the range of different structures (aliphatic to aromatic) does not influence the conductance significantly. To rationalize this surprising result, we investigate transport through these SAMs theoretically, using both full quantum methods and a generic, independent-electron tight-binding toy model. We find that the highest occupied molecular orbital, which is largely responsible for the transport in these molecules, is always strongly localized on the thiol group. The relative insensitivity of the current density to the structure of the R group is due to a combination of the couplings between the carbon chains and the transmission inside the tail. Changing from saturated to conjugated tail groups increases the latter but decreases the former. This work indicates that significant control over SAMs largely composed of nominally insulating groups may be possible when tail groups are used that are significantly larger than those used in the experiments of Yoon et al.Chemistry and Chemical Biolog

Some open questions in TDDFT: Clues from Lattice Models and Kadanoff-Baym Dynamics

Two aspects of TDDFT, the linear response approach and the adiabatic local density approximation, are examined from the perspective of lattice models. To this end, we review the DFT formulations on the lattice and give a concise presentation of the time-dependent Kadanoff-Baym equations, used to asses the limitations of the adiabatic approximation in TDDFT. We present results for the density response function of the 3D homogeneous Hubbard model, and point out a drawback of the linear response scheme based on the linearized Sham-Schl\"uter equation. We then suggest a prescription on how to amend it. Finally, we analyze the time evolution of the density in a small cubic cluster, and compare exact, adiabatic-TDDFT and Kadanoff-Baym-Equations densities. Our results show that non-perturbative (in the interaction) adiabatic potentials can perform quite well for slow perturbations but that, for faster external fields, memory effects, as already present in simple many-body approximations, are clearly required.Comment: 15 pages, submitted to Chemical Physic

Molecule-Electrode Interface Energetics in Molecular Junction: a Transition Voltage Spectroscopy Study

We assess the performances of the transition voltage spectroscopy (TVS) method to determine the energies of the molecular orbitals involved in the electronic transport though molecular junctions. A large number of various molecular junctions made with alkyl chains but with different chemical structure of the electrode-molecule interfaces are studied. In the case of molecular junctions with clean, unoxidized electrode-molecule interfaces, i.e. alkylthiols and alkenes directly grafted on Au and hydrogenated Si, respectively, we measure transition voltages in the range 0.9 - 1.4 V. We conclude that the TVS method allows estimating the onset of the tail of the LUMO density of states, at energy located 1.0 - 1.2 eV above the electrode Fermi energy. For oxidized interfaces (e.g. the same monolayer measured with Hg or eGaIn drops, or monolayers formed on a slightly oxidized silicon substrate), lower transition voltages (0.1 - 0.6 V) are systematically measured. These values are explained by the presence of oxide-related density of states at energies lower than the HOMO-LUMO of the molecules. As such, the TVS method is a useful technique to assess the quality of the molecule-electrode interfaces in molecular junctions.Comment: Accepted for publication in J. Phys. Chem C. One pdf file including manuscript, figures and supporting informatio

Characterizing the Metal–SAM Interface in Tunneling Junctions

his paper investigates the influence of the interface between a gold or silver metal electrode and an n-alkyl SAM (supported on that electrode) on the rate of charge transport across junctions with structure Met(Au or Ag)TS/A(CH2)nH//Ga2O3/EGaIn by comparing measurements of current density, J(V), for Met/AR = Au/thiolate (Au/SR), Ag/thiolate (Ag/SR), Ag/carboxylate (Ag/O2CR), and Au/acetylene (Au/C≡CR), where R is an n-alkyl group. Values of J0 and β (from the Simmons equation) were indistinguishable for these four interfaces. Since the anchoring groups, A, have large differences in their physical and electronic properties, the observation that they are indistinguishable in their influence on the injection current, J0 (V = 0.5) indicates that these four Met/A interfaces do not contribute to the shape of the tunneling barrier in a way that influences J(V).Chemistry and Chemical Biolog

Modeling Molecular Junctions: Weak and Strong Coupling Regimes

Electron transport through single molecule connected to the electrodes is an interesting problem from a fundamental point of view, and because of possible applications. From the theoretical point of view, the hope is that understanding the transport phenomena in such systems enables us to explain measurements and develop devices with new functionalities. In this thesis, different theoretical approaches are presented to address the characteristics of the molecular devices with electrical and optical probes. We have combined the non-equilibrium Green's function formalism with density functional theory (DFT) to address molecular junctions in which Coulomb correlations play a major role. An important issue in the field is the determination of the molecular levels, which contribute to transport. We have investigated the opportunities and limitations of Transition Voltage Spectroscopy (TVS) which has been advocated as a method to determine these molecular level positions without applying large voltages. We also studied a series of molecules, used recently in a self-assembled monolayer experiment, to rationalize the effects of the molecular structure on transport. Finally, we have analyzed the Raman response of several molecules in different charge states and suggested experiments in which these states could be identified using the Raman technique.Quantum NanoScienceApplied Science

Unsur timbal (pb) pada tanaman kangkung di tiga pasar tradisional kecamatan Cilandak, Jakarta Selatan

Sayuran kangkung (Ipomoea sp.) merupakan tanaman yang biasa dikonsumsi masyarakat. Sistem penanaman, pendistribusian dan penjualan yang tidak terjaga membuat sayuran mudah tercemar oleh polusi dilingkungan, salah satunya unsur timbal. Penelitian ini dilakukan untuk mengetahui kadar unsur Pb pada sayuran kangkung yang dijual di tiga pasar tradisional Kecamatan Cilandak, Jakarta Selatan. Penelitian ini dilakukan sejak bulan Februari � Maret 2014 dengan menggunakan alat Spektrofotometer Serapan Atom (SSA) metode flame. Analisis data dengan menggunakan Analisi Varians (ANOVA) dengan tingkat kepercayaan 95%. Bila terdapat perbedaan, maka dilanjutkan dengan uji Duncan Multiple Range Test. Uji MTI untuk mengetahui maksimal pengkonsumsian kangkung dengan kadar unsur tertentu dengan perkiraan berat badan 60 kg. Berdasarkan hasil penelitian, kadar unsur timbal pada sayuran kangkung di tiga pasar tradisional Kecamatan Cilandak berkisar antara 1,22 � 22,06 mg/kg. Tidak ada pengaruh yang signifikan terhadap ketiga lokasi pasar tradisional Kecamatan Cilandak. Organ akar memiliki kadar unsur timbal yang tinggi dibandingkan kadar pada daun dan batang. Seluruh sampel uji memiliki kadar unsur timbal diatas ambang batas maksimum SNI 7387:2009 sebesar 0,5mg/kg sehingga tidak aman dikonsumsi. Rata-rata berat maksimum kangkung pada tiga pasar tradisional di Kecamatan Cilandak yang boleh dikonsumsi per minggu pada organ daun dan batang berkisar antara 0,1492 � 0,6032 kg

Density functional theory based many-body analysis of electron transport through molecules

We present a method which uses density functional theory (DFT) to treat transport through a single molecule connected to two conducting leads for the weak and intermediate coupling. This case is not accessible to standard nonequilibrium Green’s function calculations. Our method is based on a mapping of the Hamiltonian on the molecule to a limited set of many-body eigenstates. This generates a many-body Hamiltonian with parameters obtained from ground-state local (spin) density approximation-DFT calculations. We then calculate the transport using many-body Green’s function theory. We compare our results with existing density matrix renormalization group calculations for spinless and for spin-1/2 fermion chains and find good agreement.QN/Quantum NanoscienceApplied Science